I have created a platformer which currently has the features listed below. I would greatly appreciate any further ideas which I could implement! (I don't play a lot of games which is why I require help)

 -- Walking/jumping/movement
 -- player can shoot lasers
 -- enemies also walk, fly, and shoot lasers
 -- water (you can swim in this)
 -- mud (slows you down on contact, and stops you from jumping)
 -- ladders
 -- damage when falling from a large height, unless falling into water
 -- moving platforms
 -- springboards (jumping on them shoot you into the air)
 -- growing platforms (allow you to reach new places)
 -- key and door system
 -- gem and coin collection system