Jedi Knight: Dark Forces 2 Easter Egg - Become Dark Jedi on Sulon

Once you recieve your lightsaber on Sulon, attack Weegee, the family droid. Eventually (after an incredible amount of time, he has many times more health than even Jerec) he will die, and Rahn will give an altered version of his 'Dark Jedi' monologue, and you will switch allegiance completely and irrevocably to the Dark Side.
(note: using the 'red5' cheat code and planting sets of 30 sequencer charges is a much faster, although more dangerous, way to kill him)