Make your way to the exit while collecting as many souls as you can. Jump using X and toggle ghost-mode using C. While in ghost-mode you can go through walls and take over enemies by touching them. When you take over an enemy you get their properties such as flight and double-jump.
Right-click game to play full-screen (if available)
X to jump
C for Ghostmode
P to pause (and see the controls)
R to restart
SHIFT to suicide/go back to the level select screen
+ to turn up the volume
- to turn down the volume
0 to mute/unmute all sounds
9 to mute/unmute the music