Easter egg

John Romero's Head
If you noclip behind the Icon Of Sin, you will see John Romero's head on stick. You can kill him to win.

Backwards Tongue
When you teleport into the huge room with the Icon Of Sin, you hear a weird, unrecognizable noise. If you play the noise backward, it says "To win the game you must kill me, John Romero".

SS men
On map 31 and 32 SSmen from Wolfenstein 3D can be found, attacking the player.

Wolfenstein 3D
Map 31 and 32 resemble Wolfenstein 3D levels, map 31 being E1M1 and map 32 is E1M9.

Commander Keen
In the last room there are 4 Commander Keens hanging at a rope. You must kill them to be able to end the level.