Planescape: Torment - 1) Where you have the option of talking Vhailor, the bad-ass Mercykiller, to death by systematically dissecting his whole worldview and making him realize that his occupation, philosophy, and existence are ultimately meaningless.... and according to Mercykillers in the Smoldering Corpse Bar, he's supposed to be the living ideal of Mercykiller beliefs 2) The Memory you recall of disproving the existence of a guy you're talking to at a party and having him realize this right before popping out of existence 3) "Forgiving" Trias, the angel instead of killing him, only to have Vhailor walk right up and axe-murder him anyway 4) Taking off the rune of Torment, and using its power to bitchslap the Transcendent One at the end of the game
Riddick: Escape from BB: Crashing the ship into Hoxie's office, then setting it up for his own men to kill him. Rampaging in the riotguard, rampaging in the heavyguard, breaking into the computer core and reprogramming it to let you use machine guns, the entire level where the aliens are overruning the place and the guards are fighting for their lives.
FF7: Anytime you use Omnislash
Mortal Kombat 3: Smoke doing a multi-hit combo ending in a back-fist, Kabal doing the move where he spins someone arounds then does a multi-hit combo with his hookswords
C&C:Red Alert 2: The level where the Russians destroy the statue of liberty
Final Fantasy Legends: Fighting The Creator at the end of the game, who is very difficult to take down, and killing him in one shot with a monster that I morphed into a black knight, who used the "saw" ability