Underworld Chaos by Zelcard is a lovely retro platform-shooter, which some really cute 16-bit graphics. You take control of a wizard who needs to collect the orbs that appear within the level to open the exit.
Monsters drop down, and can be shot, and different types of potion appear to help you out. Skulls also zap all baddies at once.
There are over 40 levels and 20 types of baddies, with an arcade mode and endless mode.
Note: The game says press Y to jump, but on a qwerty keyboard it's actually Z.