Added 

Track a high score that persists across scenes and display it in the UI (10)
Add your own (copyright-free) background music to the Play scene (10)
Create a new scrolling tile sprite for the background (10)
Allow the player to control the Rocket after it's fired (10)
Create a new spaceship type (w/ new artwork) that's smaller, moves faster, and is worth more points (25)
Implement a simultaneous two-player mode (50)
- two player mode are controled by w(shoot),a,d and up(shoot),right,left key