Constant Changes Theme is pretty Easy Guys,

Every Game has Constant Changes, if the Levels Changes, Character, Colors of something, Enemies Changing

Theres a wide Field and u literally can make any type of game for this.

Or you could take it a step further and have it so that the level changes as you move, the character gains and loses powers, colors give you epilepsy, and enemy's AI shift as it learns more about the player.

Or you could do something realistic for a 24 hour jam ;)