You have to enter Down+LP+HP, on stages The Rooftop, Pit 3, and Kahn's Cave. You will turn back into the character you choose, but you stay as him when you do it in 2 player. Other than that, those are the only stages you can play as him on in 1 player.
On MK Trilogy N64. If you want to play bosses in single player game, After 2 player match is done with player 1, Don't continue with player 2, And you can play as bosses in Single player game. Codes for bosses, Motaro. Press back high kick low kick at the same time
Yeah, I just lost it for a minute, but ignore that. When you land the spear on Shao Kahn, wait for half a second before uppercutting so you can launch the spear at him while he's getting, because if you uppercut immediately, you won't be able to launch the spear.