I've managed to get the basic mechanics done today. There are enemies that roam the game world and will kill you if you touch them, checkpoints you can activate to respawn when you die, and collectible power-ups that help you deal with enemies and obstacles and allow you to access new areas. Here are the two I have implemented so far:

Fireballs can also light torches, some of which will open doors for you. How handy!

With the basic stuff in place, I'll be spending Day 2 expanding out the game world, and adding new enemies, powers, obstacles etc. Then it'll be on to the polish stuff like music, sound effects, and some snazzy particles, and if I'm happy with it, I can hopefully submit to Compo this time!