There are 4 coloured Doors in Dr Lunatic, Red, Green, Blue and Yellow/blank. These disappear when approached with the corresponding Keys. Red, Green and Blue keys can open as many doors as necessary, but yellow keys are used up on use. The Item Editor can create other kinds of Doors, but this requires extra work on the Builder's part, as they need to make the specials that recognize the keys. It is also possible to create "global doors" that can be opened from a key collected in another level!