How to add a new Pokémon species

Despite the persistent rumors about an incredibly strong third form of Mew hiding somewhere, it actually wasn't possible to catch it... OR WAS IT? In this tutorial, we will add a new Pokémon species to the game.

Content

The Graphics
The Data
Appendix

The Graphics

We will start by copying the folder containing the sprites for Mewtwo and rename it to mewthree (pretty meta huh?):

cp -r graphics/pokemon/mewtwo graphics/pokemon/mewthree

1. Edit the sprites

Let's edit the sprites. Start your favourite image editor (I have used GIMP) and change anim_front.png, front.png and back.png to meet your expectations. Make sure that you are using the indexed mode and you have limited yourself to 14 colors! Put the RGB values of your colors into normal.pal between the first and the last color and the RGB values for the shiny version into shiny.pal. Edit footprint.png using two colors in indexed mode, black and white. Finally, edit icon.png. Notice, that the icon will use one of three predefined palettes instead of normal.pal.

2. Register the sprites

Sadly, just putting the image files into the graphics folder is not enough. To use the sprites we have to register them, which is kind of tedious. First, create constants for the file paths. Edit include/graphics.h:

 extern const u8 gMonFootprint_Chimecho[];
+extern const u32 gMonFrontPic_Mewthree[];
+extern const u32 gMonPalette_Mewthree[];
+extern const u32 gMonBackPic_Mewthree[];
+extern const u32 gMonShinyPalette_Mewthree[];
+extern const u32 gMonStillFrontPic_Mewthree[];
+extern const u8 gMonIcon_Mewthree[];
+extern const u8 gMonFootprint_Mewthree[];
 extern const u32 gMonPic_Egg[];

Now link the graphic files. Edit src/data/graphics/pokemon.h:

 const u8 gMonFootprint_Chimecho[] = INCBIN_U8("graphics/pokemon/chimecho/footprint.1bpp");

+const u32 gMonStillFrontPic_Mewthree[] = INCBIN_U32("graphics/pokemon/mewthree/front.4bpp.lz");
+const u32 gMonPalette_Mewthree[] = INCBIN_U32("graphics/pokemon/mewthree/normal.gbapal.lz");
+const u32 gMonBackPic_Mewthree[] = INCBIN_U32("graphics/pokemon/mewthree/back.4bpp.lz");
+const u32 gMonShinyPalette_Mewthree[] = INCBIN_U32("graphics/pokemon/mewthree/shiny.gbapal.lz");
+const u8 gMonIcon_Mewthree[] = INCBIN_U8("graphics/pokemon/mewthree/icon.4bpp");
+const u8 gMonFootprint_Mewthree[] = INCBIN_U8("graphics/pokemon/mewthree/footprint.1bpp");

 const u32 gMonStillFrontPic_Egg[] = INCBIN_U32("graphics/pokemon/egg/front.4bpp.lz");

The animated front picture is still missing. Edit src/anim_mon_front_pics.c:

 const u32 gMonFrontPic_Chimecho[] = INCBIN_U32("graphics/pokemon/chimecho/anim_front.4bpp.lz");
+const u32 gMonFrontPic_Mewthree[] = INCBIN_U32("graphics/pokemon/mewthree/anim_front.4bpp.lz");

 const u32 gMonFrontPic_Egg[] = INCBIN_U32("graphics/pokemon/egg/anim_front.4bpp.lz");

3. Animate the sprites

You can define the animation order, in which the sprites will be shown. The first number is the sprite index (so 0 or 1) and the second number is the number of frames the sprite will be visible. Edit src/data/pokemon_graphics/front_pic_anims.h:

 ...
 static const union AnimCmd sAnim_CHIMECHO_1[] =
 {
     ANIMCMD_FRAME(0, 15),
     ...
     ANIMCMD_END,
 };

+static const union AnimCmd sAnim_MEWTHREE_1[] =
+{
+    ANIMCMD_FRAME(1, 30),
+    ANIMCMD_FRAME(0, 20),
+    ANIMCMD_END,
+};

 static const union AnimCmd sAnim_EGG_1[] =
 {
 ...
 
 static const union AnimCmd *const sAnims_CHIMECHO[] ={
     sAnim_GeneralFrame0,
     sAnim_CHIMECHO_1,
 };

+static const union AnimCmd *const sAnims_MEWTHREE[] ={
+    sAnim_GeneralFrame0,
+    sAnim_MEWTHREE_1,
+};

 static const union AnimCmd *const sAnims_EGG[] ={
     sAnim_GeneralFrame0,
     sAnim_EGG_1,
 };
 ...
 const union AnimCmd *const *const gMonFrontAnimsPtrTable[] =
 {
     ANIM_CMD(NONE),
     ANIM_CMD(BULBASAUR),
     ...
     ANIM_CMD(CHIMECHO),
+    ANIM_CMD(MEWTHREE),
     ANIM_CMD(EGG),
     ...
};

Because you are limited to two frames, there are already predefined animations, describing translations, rotations, scalings or color changes. Edit src/pokemon_animation.c:

 static const u8 sSpeciesToBackAnimSet[] =
 {
     [SPECIES_BULBASAUR] = BACK_ANIM_DIP_RIGHT_SIDE,
     ...
     [SPECIES_CHIMECHO] = BACK_ANIM_CONCAVE_DOWN_ARC_SWAY_LARGE,
+    [SPECIES_MEWTHREE] = BACK_ANIM_GROW_2,
 };

If you want your Pokémon to fly above the ground, you can add an entry to gEnemyMonElevation. Edit src/data/pokemon_graphics/enemy_mon_elevation.h:

 const u8 gEnemyMonElevation[NUM_SPECIES] =
 {
     [SPECIES_BUTTERFREE] = 8,
     ...
     [SPECIES_CHIMECHO] = 12,
+    [SPECIES_MEWTHREE] = 6,
 };

4. Update the tables

Edit src/data/pokemon_graphics/front_pic_table.c:

 const struct CompressedSpriteSheet gMonFrontPicTable[] =
 {
     SPECIES_SPRITE(NONE, gMonFrontPic_CircledQuestionMark),
     SPECIES_SPRITE(BULBASAUR, gMonFrontPic_Bulbasaur),
     ...
     SPECIES_SPRITE(CHIMECHO, gMonFrontPic_Chimecho),
+    SPECIES_SPRITE(MEWTHREE, gMonFrontPic_Mewthree),
     SPECIES_SPRITE(EGG, gMonFrontPic_Egg),
     ...
};

Edit src/data/pokemon_graphics/still_front_pic_table.c:

 const struct CompressedSpriteSheet gMonStillFrontPicTable[] =
 {
     SPECIES_SPRITE(NONE,          gMonStillFrontPic_CircledQuestionMark),
     SPECIES_SPRITE(BULBASAUR,     gMonStillFrontPic_Bulbasaur),
     ...
     SPECIES_SPRITE(CHIMECHO,      gMonStillFrontPic_Chimecho),
+    SPECIES_SPRITE(MEWTHREE,      gMonStillFrontPic_Mewthree),
     SPECIES_SPRITE(EGG,           gMonStillFrontPic_Egg),
     ...
 };

Edit src/data/pokemon_graphics/front_pic_coordinates.h:

 const struct MonCoords gMonFrontPicCoords[] =
 {
     ...
     [SPECIES_CHIMECHO] =
     {
         .size = 0x37,
         .y_offset = 0x06,
     },
+    [SPECIES_MEWTHREE] =
+    {
+        .size = 0x88,
+        .y_offset = 0x00,
+    },
     [SPECIES_EGG] =
     {
         .size = 0x33,
         .y_offset = 0x14,
     },
     ...
 };

Edit src/data/pokemon_graphics/back_pic_table.h:

 const struct CompressedSpriteSheet gMonBackPicTable[] =
 {
     SPECIES_SPRITE(NONE, gMonBackPic_CircledQuestionMark),
     SPECIES_SPRITE(BULBASAUR, gMonBackPic_Bulbasaur),
     ...
     SPECIES_SPRITE(CHIMECHO, gMonBackPic_Chimecho),
+    SPECIES_SPRITE(MEWTHREE, gMonBackPic_Mewthree),
     SPECIES_SPRITE(EGG, gMonStillFrontPic_Egg),
     ...
};

Edit src/data/pokemon_graphics/back_pic_coordinates.h:

 const struct MonCoords gMonBackPicCoords[] =
 {
     ...
     [SPECIES_CHIMECHO] =
     {
         .size = 0x47,
         .y_offset = 0x07,
     },
+    [SPECIES_MEWTHREE] =
+    {
+        .size = 0x78,
+        .y_offset = 0x01,
+    },
     [SPECIES_EGG] =
     {
         .size = 0x36,
         .y_offset = 0x0a,
     },
     ...
 };

Edit src/data/pokemon_graphics/footprint_table.h:

 const u8 *const gMonFootprintTable[] =
 {
     [SPECIES_NONE] = gMonFootprint_Bulbasaur,
     [SPECIES_BULBASAUR] = gMonFootprint_Bulbasaur,
     ...
     [SPECIES_CHIMECHO] = gMonFootprint_Chimecho,
+    [SPECIES_MEWTHREE] = gMonFootprint_Mewthree,
     [SPECIES_EGG] = gMonFootprint_Bulbasaur,
 };

Edit src/data/pokemon_graphics/palette_table.h:

 const struct CompressedSpritePalette gMonPaletteTable[] =
 {
    SPECIES_PAL(NONE, gMonPalette_CircledQuestionMark),
    SPECIES_PAL(BULBASAUR, gMonPalette_Bulbasaur),
    ...
    SPECIES_PAL(CHIMECHO, gMonPalette_Chimecho),
+   SPECIES_PAL(MEWTHREE, gMonPalette_Mewthree),
    SPECIES_PAL(EGG, gMonPalette_Egg),
    ...
};

Edit src/data/pokemon_graphics/shiny_palette_table.h:

const struct CompressedSpritePalette gMonShinyPaletteTable[] =
{
     SPECIES_SHINY_PAL(NONE, gMonShinyPalette_CircledQuestionMark),
     SPECIES_SHINY_PAL(BULBASAUR, gMonShinyPalette_Bulbasaur),
     ...
     SPECIES_SHINY_PAL(CHIMECHO, gMonShinyPalette_Chimecho),
+    SPECIES_SHINY_PAL(MEWTHREE, gMonShinyPalette_Mewthree),
     SPECIES_SHINY_PAL(EGG, gMonPalette_Egg),
     ...
};

Edit src/pokemon_icon.c:

 const u8 *const gMonIconTable[] =
 {
     [SPECIES_NONE] = gMonIcon_Bulbasaur,
     ...
     [SPECIES_CHIMECHO] = gMonIcon_Chimecho,
+    [SPECIES_MEWTHREE] = gMonIcon_Mewthree,
     [SPECIES_EGG] = gMonIcon_Egg,
     ...
     [SPECIES_UNOWN_QMARK] = gMonIcon_UnownQuestionMark,
 };

 const u8 gMonIconPaletteIndices[] =
 {
     [SPECIES_NONE] = 0,
     ...
     [SPECIES_CHIMECHO] = 0,
+    [SPECIES_MEWTHREE] = 2,
     [SPECIES_EGG] = 1,
     ...
     [SPECIES_UNOWN_QMARK] = 0,
 };

Here, you can choose between the three icon palettes 0, 1 and 2. Open some other icon files to find out which palette suits your icon best.

The Data

Our plan is as simple as it is brilliant: clone Mewtwo... and make it even stronger!

1. Declare a species constant

Our first step towards creating a new digital lifeform is to define its own species constant. Edit include/constants/species.h:

 #ifndef GUARD_CONSTANTS_SPECIES_H
 #define GUARD_CONSTANTS_SPECIES_H

 #define SPECIES_NONE 0
 #define SPECIES_BULBASAUR 1
 ...
 #define SPECIES_CHIMECHO 411
+#define SPECIES_MEWTHREE 412
-#define SPECIES_EGG 412
+#define SPECIES_EGG 413

-#define SPECIES_UNOWN_B 413
+#define SPECIES_UNOWN_B 414
 ...
-#define SPECIES_UNOWN_QMARK 439
+#define SPECIES_UNOWN_QMARK 440

Remember to increase the value of all species constants after Mewthree until SPECIES_UNOWN_QMARK by one.

2. Devise a name

This name will be displayed in the game. It may be different than the identifier of the species constant, especially when there are special characters involved. Edit src/data/text/species_names.h:

 const u8 gSpeciesNames[][POKEMON_NAME_LENGTH + 1] = {
     [SPECIES_NONE] = _("??????????"),
     [SPECIES_BULBASAUR] = _("BULBASAUR"),
     ... 
     [SPECIES_CHIMECHO] = _("CHIMECHO"),
+    [SPECIES_MEWTHREE] = _("MEWTHREE"),
 };

The _() underscore function doesn't really exist - it's a convention borrowed from GNU gettext to let preproc know this is text to be converted to the custom encoding used by the Gen 3 Pokemon games.

3. Define its Pokédex entry

First, we will need to add new index constants for its Pokédex entry. The index constants are divided into the Hoenn Pokédex, which contains all Pokémon native to the Hoenn region, and the national Pokédex containing all known Pokémon, which can be received after entering the hall of fame for the first time. Edit include/constants/species.h:

 // National Dex Index Defines

 #define NATIONAL_DEX_NONE 0
 #define NATIONAL_DEX_BULBASAUR 1
 ...
 #define NATIONAL_DEX_CELEBI 251

-#define NATIONAL_DEX_OLD_UNOWN_B 387
+#define NATIONAL_DEX_OLD_UNOWN_B 388
 ...
-#define NATIONAL_DEX_OLD_UNOWN_Z 411
+#define NATIONAL_DEX_OLD_UNOWN_Z 412

 #define NATIONAL_DEX_TREECKO 252
 ...
 #define NATIONAL_DEX_DEOXYS 386
 #define NATIONAL_DEX_CHIMECHO 358
+#define NATIONAL_DEX_MEWTHREE 387
 
 // Hoenn Dex Index Defines
 #define HOENN_DEX_NONE 0
 #define HOENN_DEX_BULBASAUR 203
 ...
 #define HOENN_DEX_CELEBI 386
+#define HOENN_DEX_MEWTHREE 387
 
-#define HOENN_DEX_OLD_UNOWN_B 387
+#define HOENN_DEX_OLD_UNOWN_B 388
 ...
-#define HOENN_DEX_OLD_UNOWN_Z 411
+#define HOENN_DEX_OLD_UNOWN_Z 412

Edit src/pokemon.c:

 const u16 gSpeciesToHoennPokedexNum[] = // Assigns all species to the Hoenn Dex Index (Summary No. for Hoenn Dex)
 {
     SPECIES_TO_HOENN(BULBASAUR),
     ...
     SPECIES_TO_HOENN(CHIMECHO),
+    SPECIES_TO_HOENN(MEWTHREE),
 };

 const u16 gSpeciesToNationalPokedexNum[] = // Assigns all species to the National Dex Index (Summary No. for National Dex)
 {
     SPECIES_TO_NATIONAL(BULBASAUR),
     ...
+    SPECIES_TO_NATIONAL(MEWTHREE),
 };

 const u16 gHoennToNationalOrder[] = // Assigns Hoenn Dex Pokémon (Using National Dex Index)
 {
     HOENN_TO_NATIONAL(TREECKO),
     ...
     HOENN_TO_NATIONAL(CELEBI),
+    HOENN_TO_NATIONAL(MEWTHREE),
     HOENN_TO_NATIONAL(OLD_UNOWN_B),
     ...
     HOENN_TO_NATIONAL(OLD_UNOWN_Z),
 };
 
 ...
 static const u8 sMonFrontAnimIdsTable[] =
 {
     [SPECIES_BULBASAUR - 1] = 0x06,
     ...
     [SPECIES_CHIMECHO - 1] = 0x1d,
+    [SPECIES_MEWTHREE - 1] = 0x09,
 };

Now we can define the actual text of the Pokédex entry. Append to src/data/pokemon/pokedex_text.h:

const u8 gMewthreePokedexText[] = _(
    "The rumors became true.\n"
    "This is Mews final form.\n"
    "Its power level is over 9000.\n"
    "Has science gone too far?");

Finally, we will add the Pokédex entry for Mewthree and link the text to it. Edit src/data/pokemon/pokedex_entries.h:

 const struct PokedexEntry gPokedexEntries[] =
 {
     ...
     [NATIONAL_DEX_DEOXYS] =
     {
         .categoryName = _("DNA"),
         .height = 17,
         .weight = 608,
         .description = gDeoxysPokedexText,
         .pokemonScale = 256,
         .pokemonOffset = 0,
         .trainerScale = 290,
         .trainerOffset = 2,
     },
    
+    [NATIONAL_DEX_MEWTHREE] =
+    {
+        .categoryName = _("NEW SPECIES"),
+        .height = 15,
+        .weight = 330,
+        .description = gMewthreePokedexText,
+        .pokemonScale = 256,
+        .pokemonOffset = 0,
+        .trainerScale = 290,
+        .trainerOffset = 2,
+    },
 };

The values pokemonScale, pokemonOffset, trainerScale and trainerOffset are used for the height comparison figure in the Pokédex. Height and weight are specified in meters and kilograms respectively, while the last digit is the first decimal place. In Pokémon Emerald, you can sort the Pokédex by name, height or weight. Apparently, the Pokémon order is hardcoded in the game files and not calculated from their data. Therefore we have to include our new Pokémon species at the right places. While the correct position for the alphabetical order is easy to find, it can become quite tedious for height and weight. To find the right position for your Pokémon, you may look at the tables sorted by height and weight respectively in the appendix. Edit src/data/pokemon/pokedex_orders.h:

 const u16 gPokedexOrder_Alphabetical[] =
 {
     ...
     NATIONAL_DEX_MEW,
+    NATIONAL_DEX_MEWTHREE,
     NATIONAL_DEX_MEWTWO,
     ...
 };

 const u16 gPokedexOrder_Weight[] =
 {
     ...
     NATIONAL_DEX_CRAWDAUNT,
+    NATIONAL_DEX_MEWTHREE,
     NATIONAL_DEX_DUGTRIO,
     ...
 };
 
 const u16 gPokedexOrder_Height[] =
 {
     ...
     NATIONAL_DEX_XATU,
+    NATIONAL_DEX_MEWTHREE,
     NATIONAL_DEX_CRADILY,
     ...
 };

4. Define its base stats

Edit src/data/pokemon/base_stats.h:

 const struct BaseStats gBaseStats[] =
 {
     [SPECIES_NONE] = {0},
     ...
+    [SPECIES_MEWTHREE] =
+    {
+       .baseHP        = 106,
+       .baseAttack    = 150,
+       .baseDefense   = 70,
+       .baseSpeed     = 140,
+       .baseSpAttack  = 194,
+       .baseSpDefense = 120,
+       .type1 = TYPE_PSYCHIC,
+       .type2 = TYPE_PSYCHIC,
+       .catchRate = 3,
+       .expYield = 255,
+       .evYield_HP        = 0,
+       .evYield_Attack    = 0,
+       .evYield_Defense   = 0,
+       .evYield_Speed     = 0,
+       .evYield_SpAttack  = 3,
+       .evYield_SpDefense = 0,
+       .item1 = ITEM_NONE,
+       .item2 = ITEM_NONE,
+       .genderRatio = MON_GENDERLESS,
+       .eggCycles = 120,
+       .friendship = 0,
+       .growthRate = GROWTH_SLOW,
+       .eggGroup1 = EGG_GROUP_UNDISCOVERED,
+       .eggGroup2 = EGG_GROUP_UNDISCOVERED,
+       .abilities = {ABILITY_INSOMNIA, ABILITY_NONE},
+       .safariZoneFleeRate = 0,
+       .bodyColor = BODY_COLOR_PURPLE,
+       .noFlip = FALSE,
+    },
 };

The . is the structure reference operator in C to refer to the member object of the structure BaseStats. Notice how I also changed the ability to ABILITY_INSOMNIA, so our little monster doesn't even need to sleep anymore. You can find the abilities for example here include/constants/abilities.h and here src/data/text/abilities.h.

5. Delimit the moveset

Let's begin with the moves that can be learned by leveling up. Append to src/data/pokemon/level_up_learnsets.h:

static const u16 sMewthreeLevelUpLearnset[] = {
    LEVEL_UP_MOVE( 1, MOVE_CONFUSION),
    LEVEL_UP_MOVE( 1, MOVE_DISABLE),
    LEVEL_UP_MOVE(11, MOVE_BARRIER),
    LEVEL_UP_MOVE(22, MOVE_SWIFT),
    LEVEL_UP_MOVE(33, MOVE_PSYCH_UP),
    LEVEL_UP_MOVE(44, MOVE_FUTURE_SIGHT),
    LEVEL_UP_MOVE(55, MOVE_MIST),
    LEVEL_UP_MOVE(66, MOVE_PSYCHIC),
    LEVEL_UP_MOVE(77, MOVE_AMNESIA),
    LEVEL_UP_MOVE(88, MOVE_RECOVER),
    LEVEL_UP_MOVE(99, MOVE_SAFEGUARD),
    LEVEL_UP_END
};

Again, we need to register the learnset. Edit src/data/pokemon/level_up_learnsets_pointers.h:

 const u16 *const gLevelUpLearnsets[NUM_SPECIES] =
 {
     [SPECIES_NONE] = sBulbasaurLevelUpLearnset,
     [SPECIES_BULBASAUR] = sBulbasaurLevelUpLearnset,
     ...
     [SPECIES_CHIMECHO] = sChimechoLevelUpLearnset,
+    [SPECIES_MEWTHREE] = sMewthreeLevelUpLearnset,
 };

Edit src/data/pokemon/tmhm_learnsets.h:

 const u32 gTMHMLearnsets[][2] =
 {
     [SPECIES_NONE]        = TMHM_LEARNSET(0),
     ...
     [SPECIES_CHIMECHO]    = TMHM_LEARNSET(TMHM(TM04_CALM_MIND)
                                         ...
                                         | TMHM(HM05_FLASH)),

+    [SPECIES_MEWTHREE]   = TMHM_LEARNSET(TMHM(TM01_FOCUS_PUNCH)
+                                        | TMHM(TM03_WATER_PULSE)
+                                        | TMHM(TM04_CALM_MIND)
+                                        | TMHM(TM06_TOXIC)
+                                        | TMHM(TM07_HAIL)
+                                        | TMHM(TM08_BULK_UP)
+                                        | TMHM(TM10_HIDDEN_POWER)
+                                        | TMHM(TM11_SUNNY_DAY)
+                                        | TMHM(TM12_TAUNT)
+                                        | TMHM(TM13_ICE_BEAM)
+                                        | TMHM(TM14_BLIZZARD)
+                                        | TMHM(TM15_HYPER_BEAM)
+                                        | TMHM(TM16_LIGHT_SCREEN)
+                                        | TMHM(TM17_PROTECT)
+                                        | TMHM(TM18_RAIN_DANCE)
+                                        | TMHM(TM20_SAFEGUARD)
+                                        | TMHM(TM21_FRUSTRATION)
+                                        | TMHM(TM22_SOLARBEAM)
+                                        | TMHM(TM23_IRON_TAIL)
+                                        | TMHM(TM24_THUNDERBOLT)
+                                        | TMHM(TM25_THUNDER)
+                                        | TMHM(TM26_EARTHQUAKE)
+                                        | TMHM(TM27_RETURN)
+                                        | TMHM(TM29_PSYCHIC)
+                                        | TMHM(TM30_SHADOW_BALL)
+                                        | TMHM(TM31_BRICK_BREAK)
+                                        | TMHM(TM32_DOUBLE_TEAM)
+                                        | TMHM(TM33_REFLECT)
+                                        | TMHM(TM34_SHOCK_WAVE)
+                                        | TMHM(TM35_FLAMETHROWER)
+                                        | TMHM(TM37_SANDSTORM)
+                                        | TMHM(TM38_FIRE_BLAST)
+                                        | TMHM(TM39_ROCK_TOMB)
+                                        | TMHM(TM40_AERIAL_ACE)
+                                        | TMHM(TM41_TORMENT)
+                                        | TMHM(TM42_FACADE)
+                                        | TMHM(TM43_SECRET_POWER)
+                                        | TMHM(TM44_REST)
+                                        | TMHM(TM48_SKILL_SWAP)
+                                        | TMHM(TM49_SNATCH)
+                                        | TMHM(HM04_STRENGTH)
+                                        | TMHM(HM05_FLASH)
+                                        | TMHM(HM06_ROCK_SMASH)),
 };

Edit src/data/pokemon/tutor_learnsets.h:

 static const u32 sTutorLearnsets[] =
 {
     [SPECIES_NONE]             = TUTOR_LEARNSET(0),
     ...
     [SPECIES_CHIMECHO]         = TUTOR_LEARNSET(TUTOR(MOVE_DOUBLE_EDGE)
                                               ...
                                               | TUTOR(MOVE_DEFENSE_CURL)),
     
+    [SPECIES_MEWTHREE]           = TUTOR_LEARNSET(TUTOR(MOVE_MEGA_PUNCH)
+                                              | TUTOR(MOVE_MEGA_KICK)
+                                              | TUTOR(MOVE_BODY_SLAM)
+                                              | TUTOR(MOVE_DOUBLE_EDGE)
+                                              | TUTOR(MOVE_COUNTER)
+                                              | TUTOR(MOVE_SEISMIC_TOSS)
+                                              | TUTOR(MOVE_MIMIC)
+                                              | TUTOR(MOVE_METRONOME)
+                                              | TUTOR(MOVE_DREAM_EATER)
+                                              | TUTOR(MOVE_THUNDER_WAVE)
+                                              | TUTOR(MOVE_SUBSTITUTE)
+                                              | TUTOR(MOVE_DYNAMIC_PUNCH)
+                                              | TUTOR(MOVE_PSYCH_UP)
+                                              | TUTOR(MOVE_SNORE)
+                                              | TUTOR(MOVE_ICY_WIND)
+                                              | TUTOR(MOVE_ENDURE)
+                                              | TUTOR(MOVE_MUD_SLAP)
+                                              | TUTOR(MOVE_ICE_PUNCH)
+                                              | TUTOR(MOVE_SWAGGER)
+                                              | TUTOR(MOVE_SLEEP_TALK)
+                                              | TUTOR(MOVE_SWIFT)
+                                              | TUTOR(MOVE_THUNDER_PUNCH)
+                                              | TUTOR(MOVE_FIRE_PUNCH)),
 };

If you want to create a Pokémon which can breed, you will need to edit src/data/pokemon/egg_moves.h.

6. Define its cry

In sound/direct_sound_data.inc.

	.align 2
   Cry_Chimecho::
	.incbin "sound/direct_sound_samples/cries/chimecho.bin"

+ 	.align 2
+  Cry_Mewthree::
+	.incbin "sound/direct_sound_samples/cries/mewthree.bin"

And linking it in sound/cry_tables.inc. cry2 in particular is for reversed cries for moves like Growl

...
	cry Cry_Latios  @ 869EEF4
	cry Cry_Jirachi  @ 869EF00
	cry Cry_Deoxys  @ 869EF0C
	cry Cry_Chimecho  @ 869EF18
+       cry Cry_Mewthree  @ 869EF18
...
	cry2 Cry_Latios  @ 86A0124
	cry2 Cry_Jirachi  @ 86A0130
	cry2 Cry_Deoxys  @ 86A013C
	cry2 Cry_Chimecho  @ 86A0148
+       cry2 Cry_Mewthree  @ 86A0148

And finally, edit src/data/pokemon/cry_ids.h:

 const u16 gSpeciesIdToCryId[] =
 {
     [SPECIES_TREECKO - 277] = 273,
     ...
     [SPECIES_CHIMECHO - 277] = 387,
+    [SPECIES_MEWTHREE - 277] = 388,
 };

Mon cries are 10512Hz. Make sure to put the aif file in the directory sound/direct_sound_samples/cries

Higher frequencies may be ruined by compression. To have the cries uncompressed, follow this , then clear out the old sound bins

7. Define the Evolutions

We want Mewthree to evolve from Mewtwo by reaching level 100. Edit src/data/pokemon/evolution.h:

     [SPECIES_METANG]     = {{EVO_LEVEL, 45, SPECIES_METAGROSS}},
+    [SPECIES_MEWTWO]     = {{EVO_LEVEL, 100, SPECIES_MEWTHREE}},
 };

8. Easy Chat about your Pokémon

Edit src/data/easy_chat/easy_chat_words_by_letter.h:

 const u16 gEasyChatWordsByLetter_M[] = {
     EC_MOVE2(MACH_PUNCH),
     ...
     EC_POKEMON2(MEW),
+    EC_POKEMON2(MEWTHREE),
     EC_POKEMON2(MEWTWO),
     ...
     EC_WORD_MYSTERY,
 };

9. Make it appear!

Now Mewthree really does slumber in the games code - but we won't know until we make him appear somewhere! The legend tells that Mewthree is hiding somewhere in Petalburg Woods... Edit src/data/wild_encounters.json:

         {
           "map": "MAP_PETALBURG_WOODS",
           "base_label": "gPetalburgWoods",
           "land_mons": {
             "encounter_rate": 20,
             "mons": [
               {
                 "min_level": 5,
                 "max_level": 5,
                 "species": "SPECIES_POOCHYENA"
               },
               {
                 "min_level": 5,
                 "max_level": 5,
                 "species": "SPECIES_WURMPLE"
               },
               {
                 "min_level": 5,
                 "max_level": 5,
                 "species": "SPECIES_SHROOMISH"
               },
               {
-                "min_level": 6,
-                "max_level": 6,
-                "species": "SPECIES_POOCHYENA"
+                "min_level": 5,
+                "max_level": 5,
+                "species": "SPECIES_MEWTHREE"
               },
               ...
        }

Congratulations, you have created your own personal pocket monster! You may call yourself a mad scientist now.

Appendix

Available Battle Animations

BACK_ANIM_NONE
BACK_ANIM_H_SLIDE_QUICK
BACK_ANIM_H_SLIDE
BACK_ANIM_H_SLIDE_WITH_V_COMPRESS_1
BACK_ANIM_H_SLIDE_WITH_V_COMPRESS_2
BACK_ANIM_SHRINK_GROW_1
BACK_ANIM_GROW_1
BACK_ANIM_CIRCLE_MOVE_COUNTERCLOCKWISE
BACK_ANIM_HORIZONTAL_SHAKE
BACK_ANIM_VERTICAL_SHAKE
BACK_ANIM_V_SHAKE_WITH_H_SLIDE
BACK_ANIM_VERTICAL_STRETCH
BACK_ANIM_HORIZONTAL_STRETCH
BACK_ANIM_GROW_2
BACK_ANIM_V_SHAKE_WITH_PAUSE
BACK_ANIM_CIRCLE_MOVE_CLOCKWISE
BACK_ANIM_CONCAVE_DOWN_ARC_SWAY_SMALL
BACK_ANIM_CONCAVE_DOWN_ARC_SWAY_LARGE
BACK_ANIM_CONCAVE_UP_ARC_SWAY_LARGE
BACK_ANIM_DIP_RIGHT_SIDE
BACK_ANIM_SHRINK_GROW_2
BACK_ANIM_JOLT_RIGHT
BACK_ANIM_FLASH_YELLOW_WITH_SHAKE
BACK_ANIM_FADE_RED_WITH_SHAKE
BACK_ANIM_FADE_GREEN_WITH_SHAKE
BACK_ANIM_FADE_BLUE_WITH_SHAKE

Pokémon ordered by height

Pokemon	height (m)
Diglett	0.2
Natu	0.2
Azurill	0.2
Caterpie	0.3
Weedle	0.3
Pidgey	0.3
Rattata	0.3
Spearow	0.3
Paras	0.3
Magnemite	0.3
Shellder	0.3
Ditto	0.3
Eevee	0.3
Pichu	0.3
Cleffa	0.3
Igglybuff	0.3
Togepi	0.3
Sunkern	0.3
Wurmple	0.3
Taillow	0.3
Roselia	0.3
Castform	0.3
Jirachi	0.3
Pikachu	0.4
Nidoran_f	0.4
Meowth	0.4
Geodude	0.4
Krabby	0.4
Exeggcute	0.4
Cubone	0.4
Horsea	0.4
Omanyte	0.4
Mew	0.4
Bellossom	0.4
Marill	0.4
Hoppip	0.4
Wooper	0.4
Swinub	0.4
Smoochum	0.4
Torchic	0.4
Mudkip	0.4
Zigzagoon	0.4
Ralts	0.4
Shroomish	0.4
Aron	0.4
Plusle	0.4
Minun	0.4
Gulpin	0.4
Cacnea	0.4
Swablu	0.4
Barboach	0.4
Clamperl	0.4
Squirtle	0.5
Nidoran_m	0.5
Jigglypuff	0.5
Oddish	0.5
Mankey	0.5
Voltorb	0.5
Kabuto	0.5
Cyndaquil	0.5
Spinarak	0.5
Chinchou	0.5
Murkrow	0.5
Unown	0.5
Qwilfish	0.5
Phanpy	0.5
Treecko	0.5
Poochyena	0.5
Linoone	0.5
Lotad	0.5
Seedot	0.5
Surskit	0.5
Nincada	0.5
Sableye	0.5
Torkoal	0.5
Baltoy	0.5
Charmander	0.6
Kakuna	0.6
Sandshrew	0.6
Clefairy	0.6
Vulpix	0.6
Poliwag	0.6
Koffing	0.6
Goldeen	0.6
Totodile	0.6
Togetic	0.6
Mareep	0.6
Skiploom	0.6
Pineco	0.6
Snubbull	0.6
Shuckle	0.6
Teddiursa	0.6
Corsola	0.6
Remoraid	0.6
Houndour	0.6
Porygon2	0.6
Elekid	0.6
Larvitar	0.6
Celebi	0.6
Silcoon	0.6
Wingull	0.6
Whismur	0.6
Skitty	0.6
Mawile	0.6
Meditite	0.6
Electrike	0.6
Illumise	0.6
Corphish	0.6
Feebas	0.6
Shuppet	0.6
Chimecho	0.6
Wynaut	0.6
Luvdisc	0.6
Bagon	0.6
Beldum	0.6
Bulbasaur	0.7
Metapod	0.7
Raticate	0.7
Dugtrio	0.7
Growlithe	0.7
Bellsprout	0.7
Hoothoot	0.7
Misdreavus	0.7
Slugma	0.7
Tyrogue	0.7
Magby	0.7
Marshtomp	0.7
Cascoon	0.7
Swellow	0.7
Volbeat	0.7
Numel	0.7
Spoink	0.7
Trapinch	0.7
Anorith	0.7
Snorunt	0.7
Raichu	0.8
Nidorina	0.8
Zubat	0.8
Gloom	0.8
Psyduck	0.8
Machop	0.8
Farfetchd	0.8
Staryu	0.8
Jolteon	0.8
Porygon	0.8
Sentret	0.8
Flaaffy	0.8
Azumarill	0.8
Jumpluff	0.8
Aipom	0.8
Sunflora	0.8
Magcargo	0.8
Kirlia	0.8
Masquerain	0.8
Slakoth	0.8
Ninjask	0.8
Shedinja	0.8
Carvanha	0.8
Duskull	0.8
Spheal	0.8
Nidorino	0.9
Abra	0.9
Tentacool	0.9
Grimer	0.9
Magikarp	0.9
Flareon	0.9
Chikorita	0.9
Quilava	0.9
Espeon	0.9
Sneasel	0.9
Octillery	0.9
Delibird	0.9
Grovyle	0.9
Combusken	0.9
Lairon	0.9
Grumpig	0.9
Whiscash	0.9
Ivysaur	1.0
Wartortle	1.0
Beedrill	1.0
Sandslash	1.0
Wigglytuff	1.0
Parasect	1.0
Venonat	1.0
Persian	1.0
Primeape	1.0
Poliwhirl	1.0
Weepinbell	1.0
Graveler	1.0
Ponyta	1.0
Magneton	1.0
Drowzee	1.0
Marowak	1.0
Rhyhorn	1.0
Tangela	1.0
Vaporeon	1.0
Omastar	1.0
Ledyba	1.0
Umbreon	1.0
Mightyena	1.0
Beautifly	1.0
Nuzleaf	1.0
Loudred	1.0
Makuhita	1.0
Nosepass	1.0
Lunatone	1.0
Lileep	1.0
Kecleon	1.0
Relicanth	1.0
Charmeleon	1.1
Butterfree	1.1
Pidgeotto	1.1
Ninetales	1.1
Seel	1.1
Chansey	1.1
Starmie	1.1
Electabuzz	1.1
Croconaw	1.1
Ariados	1.1
Politoed	1.1
Gligar	1.1
Piloswine	1.1
Donphan	1.1
Delcatty	1.1
Spinda	1.1
Vibrava	1.1
Altaria	1.1
Crawdaunt	1.1
Banette	1.1
Sealeo	1.1
Shelgon	1.1
Fearow	1.2
Vileplume	1.2
Slowpoke	1.2
Muk	1.2
Electrode	1.2
Lickitung	1.2
Weezing	1.2
Seadra	1.2
Bayleef	1.2
Lanturn	1.2
Sudowoodo	1.2
Yanma	1.2
Forretress	1.2
Smeargle	1.2
Miltank	1.2
Pupitar	1.2
Dustox	1.2
Lombre	1.2
Pelipper	1.2
Breloom	1.2
Solrock	1.2
Absol	1.2
Metang	1.2
Nidoqueen	1.3
Clefable	1.3
Poliwrath	1.3
Kadabra	1.3
Gastly	1.3
Kingler	1.3
Seaking	1.3
Mr_mime	1.3
Magmar	1.3
Kabutops	1.3
Wobbuffet	1.3
Shiftry	1.3
Medicham	1.3
Cacturne	1.3
Zangoose	1.3
Nidoking	1.4
Golem	1.4
Doduo	1.4
Hitmonchan	1.4
Jynx	1.4
Tauros	1.4
Ledian	1.4
Ampharos	1.4
Quagsire	1.4
Granbull	1.4
Houndoom	1.4
Stantler	1.4
Hitmontop	1.4
Vigoroth	1.4
Walrein	1.4
Latias	1.4
Pidgeot	1.5
Venomoth	1.5
Alakazam	1.5
Machoke	1.5
Cloyster	1.5
Gengar	1.5
Hitmonlee	1.5
Scyther	1.5
Pinsir	1.5
Xatu	1.5
Girafarig	1.5
Dunsparce	1.5
Heracross	1.5
Blissey	1.5
Swampert	1.5
Ludicolo	1.5
Exploud	1.5
Manectric	1.5
Claydol	1.5
Cradily	1.5
Armaldo	1.5
Glalie	1.5
Salamence	1.5
Blastoise	1.6
Golbat	1.6
Machamp	1.6
Tentacruel	1.6
Slowbro	1.6
Haunter	1.6
Hypno	1.6
Zapdos	1.6
Noctowl	1.6
Gardevoir	1.6
Dusclops	1.6
Metagross	1.6
Charizard	1.7
Golduck	1.7
Victreebel	1.7
Rapidash	1.7
Dewgong	1.7
Articuno	1.7
Typhlosion	1.7
Skarmory	1.7
Sceptile	1.7
Swalot	1.7
Huntail	1.7
Regirock	1.7
Deoxys	1.7
Dodrio	1.8
Aerodactyl	1.8
Dratini	1.8
Meganium	1.8
Furret	1.8
Crobat	1.8
Scizor	1.8
Ursaring	1.8
Kingdra	1.8
Sharpedo	1.8
Gorebyss	1.8
Regice	1.8
Arcanine	1.9
Rhydon	1.9
Raikou	1.9
Blaziken	1.9
Camerupt	1.9
Registeel	1.9
Venusaur	2.0
Ekans	2.0
Exeggutor	2.0
Moltres	2.0
Mewtwo	2.0
Slowking	2.0
Suicune	2.0
Tyranitar	2.0
Slaking	2.0
Wailmer	2.0
Flygon	2.0
Tropius	2.0
Latios	2.0
Snorlax	2.1
Mantine	2.1
Entei	2.1
Aggron	2.1
Kangaskhan	2.2
Dragonite	2.2
Feraligatr	2.3
Hariyama	2.3
Lapras	2.5
Seviper	2.7
Arbok	3.5
Groudon	3.5
Ho_oh	3.8
Dragonair	4.0
Kyogre	4.5
Lugia	5.2
Milotic	6.2
Gyarados	6.5
Rayquaza	7.0
Onix	8.8
Steelix	9.2
Wailord	14.5

Pokémon ordered by weight

Pokemon	weight (kg)
Gastly	0.1
Haunter	0.1
Hoppip	0.5
Diglett	0.8
Castform	0.8
Igglybuff	1.0
Koffing	1.0
Skiploom	1.0
Chimecho	1.0
Misdreavus	1.0
Jirachi	1.1
Swablu	1.2
Shedinja	1.2
Togepi	1.5
Surskit	1.7
Pidgey	1.8
Sunkern	1.8
Barboach	1.9
Natu	2.0
Azurill	2.0
Spearow	2.0
Pichu	2.0
Roselia	2.0
Murkrow	2.1
Taillow	2.3
Shuppet	2.3
Exeggcute	2.5
Torchic	2.5
Lotad	2.6
Caterpie	2.9
Cleffa	3.0
Jumpluff	3.0
Weedle	3.2
Togetic	3.2
Dratini	3.3
Rattata	3.5
Wurmple	3.6
Masquerain	3.6
Qwilfish	3.9
Shellder	4.0
Ditto	4.0
Mew	4.0
Seedot	4.0
Bellsprout	4.0
Meowth	4.2
Plusle	4.2
Minun	4.2
Shroomish	4.5
Unown	5.0
Treecko	5.0
Corsola	5.0
Celebi	5.0
Spinda	5.0
Paras	5.4
Oddish	5.4
Jigglypuff	5.5
Nincada	5.5
Bellossom	5.8
Magnemite	6.0
Pikachu	6.0
Smoochum	6.0
Sentret	6.0
Chikorita	6.4
Weepinbell	6.4
Eevee	6.5
Krabby	6.5
Cubone	6.5
Swinub	6.5
Ralts	6.6
Bulbasaur	6.9
Ekans	6.9
Nidoran_f	7.0
Pineco	7.2
Feebas	7.4
Omanyte	7.5
Clefairy	7.5
Zubat	7.5
Mudkip	7.6
Mareep	7.8
Snubbull	7.8
Cyndaquil	7.9
Horsea	8.0
Marill	8.5
Wooper	8.5
Spinarak	8.5
Charmander	8.5
Sunflora	8.5
Gloom	8.6
Luvdisc	8.7
Teddiursa	8.8
Squirtle	9.0
Nidoran_m	9.0
Totodile	9.5
Wingull	9.5
Weezing	9.5
Vulpix	9.9
Metapod	9.9
Kakuna	10.0
Silcoon	10.0
Magikarp	10.0
Gulpin	10.3
Voltorb	10.4
Houndour	10.8
Ledyba	10.8
Sableye	11.0
Skitty	11.0
Meditite	11.2
Kabuto	11.5
Mawile	11.5
Corphish	11.5
Cascoon	11.5
Aipom	11.5
Chinchou	12.0
Sandshrew	12.0
Remoraid	12.0
Ninjask	12.0
Wigglytuff	12.0
Poliwag	12.4
Anorith	12.5
Banette	12.5
Venomoth	12.5
Ivysaur	13.0
Flaaffy	13.3
Poochyena	13.6
Wynaut	14.0
Dunsparce	14.0
Goldeen	15.0
Trapinch	15.0
Farfetchd	15.0
Duskull	15.0
Xatu	15.0
Electrike	15.2
Vibrava	15.3
Victreebel	15.5
Bayleef	15.8
Delibird	16.0
Whismur	16.3
Dragonair	16.5
Snorunt	16.8
Zigzagoon	17.5
Illumise	17.7
Volbeat	17.7
Raticate	18.5
Vileplume	18.6
Growlithe	19.0
Quilava	19.0
Charmeleon	19.0
Machop	19.5
Nidorino	19.5
Abra	19.5
Combusken	19.5
Psyduck	19.6
Swellow	19.8
Ninetales	19.9
Geodude	20.0
Nidorina	20.0
Poliwhirl	20.0
Kirlia	20.2
Shuckle	20.5
Altaria	20.6
Carvanha	20.8
Tyrogue	21.0
Hoothoot	21.2
Magby	21.4
Baltoy	21.5
Grovyle	21.6
Kecleon	22.0
Wartortle	22.5
Lanturn	22.5
Gorebyss	22.6
Relicanth	23.4
Elekid	23.5
Whiscash	23.6
Lileep	23.8
Numel	24.0
Slakoth	24.0
Jolteon	24.5
Flareon	25.0
Croconaw	25.0
Seadra	25.0
Espeon	26.5
Umbreon	27.0
Huntail	27.0
Mankey	28.0
Marshtomp	28.0
Sneasel	28.0
Nuzleaf	28.0
Pelipper	28.0
Beautifly	28.4
Azumarill	28.5
Octillery	28.5
Wobbuffet	28.5
Vaporeon	29.0
Beedrill	29.5
Sandslash	29.5
Parasect	29.5
Raichu	30.0
Grimer	30.0
Venonat	30.0
Ponyta	30.0
Pidgeotto	30.0
Electabuzz	30.0
Muk	30.0
Spoink	30.6
Dusclops	30.6
Medicham	31.5
Dustox	31.6
Persian	32.0
Primeape	32.0
Butterfree	32.0
Drowzee	32.4
Linoone	32.5
Porygon2	32.5
Lombre	32.5
Furret	32.5
Delcatty	32.6
Crawdaunt	32.8
Dugtrio	33.3
Phanpy	33.5
Ariados	33.5
Politoed	33.9
Staryu	34.5
Chansey	34.6
Slugma	35.0
Tangela	35.0
Omastar	35.0
Houndoom	35.0
Ledian	35.6
Slowpoke	36.0
Porygon	36.5
Mightyena	37.0
Fearow	38.0
Sudowoodo	38.0
Yanma	38.0
Seaking	39.0
Breloom	39.2
Doduo	39.2
Spheal	39.5
Pidgeot	39.5
Clefable	40.0
Latias	40.0
Manectric	40.2
Zangoose	40.3
Loudred	40.5
Kabutops	40.5
Gengar	40.5
Jynx	40.6
Noctowl	40.8
Girafarig	41.5
Bagon	42.1
Magmar	44.5
Marowak	45.0
Tentacool	45.5
Vigoroth	46.5
Blissey	46.8
Absol	47.0
Hitmontop	48.0
Alakazam	48.0
Gardevoir	48.4
Granbull	48.7
Hitmonlee	49.8
Hitmonchan	50.2
Skarmory	50.5
Cacnea	51.3
Blaziken	52.0
Sceptile	52.2
Clamperl	52.5
Seviper	52.5
Zapdos	52.6
Poliwrath	54.0
Heracross	54.0
Mr_mime	54.5
Magcargo	55.0
Pinsir	55.0
Ludicolo	55.0
Golbat	55.0
Tentacruel	55.0
Articuno	55.4
Piloswine	55.8
Scyther	56.0
Kadabra	56.5
Smeargle	58.0
Aerodactyl	59.0
Shiftry	59.6
Aron	60.0
Magneton	60.0
Nidoqueen	60.0
Kingler	60.0
Moltres	60.0
Latios	60.0
Cradily	60.4
Deoxys	60.8
Ampharos	61.5
Nidoking	62.0
Gligar	64.8
Arbok	65.0
Lickitung	65.5
Electrode	66.6
Armaldo	68.2
Machoke	70.5
Stantler	71.2
Grumpig	71.5
Larvitar	72.0
Quagsire	75.0
Crobat	75.0
Miltank	75.5
Hypno	75.6
Golduck	76.6
Cacturne	77.4
Slowbro	78.5
Typhlosion	79.5
Slowking	79.5
Starmie	80.0
Swalot	80.0
Kangaskhan	80.0
Torkoal	80.4
Swampert	81.9
Flygon	82.0
Exploud	84.0
Dodrio	85.2
Blastoise	85.5
Makuhita	86.4
Sealeo	87.6
Tauros	88.4
Sharpedo	88.8
Feraligatr	88.8
Seel	90.0
Charizard	90.5
Rapidash	95.0
Beldum	95.2
Nosepass	97.0
Venusaur	100.0
Tropius	100.0
Meganium	100.5
Salamence	102.6
Graveler	105.0
Claydol	108.0
Shelgon	110.5
Rhyhorn	115.0
Scizor	118.0
Lairon	120.0
Donphan	120.0
Dewgong	120.0
Rhydon	120.0
Exeggutor	120.0
Mewtwo	122.0
Forretress	125.8
Ursaring	125.8
Machamp	130.0
Wailmer	130.0
Slaking	130.5
Cloyster	132.5
Walrein	150.6
Pupitar	152.0
Kingdra	152.0
Solrock	154.0
Arcanine	155.0
Milotic	162.0
Lunatone	168.0
Regice	175.0
Raikou	178.0
Suicune	187.0
Entei	198.0
Ho_oh	199.0
Tyranitar	202.0
Metang	202.5
Registeel	205.0
Rayquaza	206.5
Dragonite	210.0
Onix	210.0
Lugia	216.0
Camerupt	220.0
Mantine	220.0
Lapras	220.0
Regirock	230.0
Gyarados	235.0
Hariyama	253.8
Glalie	256.5
Golem	300.0
Kyogre	352.0
Aggron	360.0
Wailord	398.0
Steelix	400.0
Snorlax	460.0
Metagross	550.0
Groudon	950.0

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