When you enter a door it will put out in a random room and lock the door behind you to either force you to complete the room or pick up an item.
Enemy Damage increases over time.
Space jump, Gravity, Screw attack, Plasma are temporary, they disappear after a certain amount of time(visual timer gauge on the hud).
Mother brain doesn't trigger the ending sequence instead its just a normal boss, the rainbow beam phase is skipped so you don't need 300 hp to beat mother brain.
Achievements system. get reward for performing various speed trick or doing weird out of place stuff.
Score system for the amount of rooms and points when killing monster or completing achievements
Difficulty selection
Time attack mode, Start with a set amount of time, gain time by racking up points or taking no damage on bosses