Here is the full list of all 13 You are Peter Shorts achievements.
Rescue all Peters in the main game
Find all diskettes
Reveal every tile on the map
Beat any difficulty in under 2 hours
Play 20 VS matches
Unlock all Peters in VS mode
Clear Easy Mode
Clear Normal Mode
Clear Hard Mode
Stand on top of the title.
Free the Alien
Get 100 KOs in Peter's Dream
Beat VS SCIENTIST in under 6 minutes