I have made a .lmp of me finishing Level 30 on ultra-violence, but you'll need Doom II 1.9 to view it. If you don't have that version of Doom II, you'll get an error like "demo is from wrong game version."
When you go first through the teleporter, the demon says, "To win the
game, you must kill me, John Romero," backwards and slowed-down
(John Romero is one of Id Software's founders). If you turn on
no-clipping mode (type idclip) and go through the middle of the
north wall (where you see the exposed brain), you can see John Romero's
head on a stake. If you shoot it, you win the game (although you should
really try to kill it without cheating). You can't see the head
on the stake without cheating.