It's 4am over here in the UK and I think it's time I get some rest. So far today I've managed to produce all the elements necessary for a basic gameplay loop, and things are finally starting to resemble an actual game (albeit a somewhat ugly one):

The player has to collect keys (which may be lying on the ground or held by enemies) and bring them back to the start in order to clear the floor. After each floor your remaining health will decrease by one (even if you took no damage), forcing you to increase the difficulty of the next floor in order to earn additional lives. Is it better to attempt lots of easy levels with minimal health, or go straight for the harder difficulty with as much as you can get?

The next step for this game is to implement the purchasable difficulty modifiers, as well as add new types of enemy. From there I can start looking at replacing some of the placeholder graphics with slightly less terrible placeholder graphics/animation, and possibly think about music/sound effects if I have time.

But first, sleep.