If you do the spear enough times, Scorpion says "get the f- over here".
If you do Noob's shadow tackle enough times, instead of pushing the shadow towards you, he shoves it and turns around and gives it the finger.
If you do the crotch punch with JC enough, he'll do a split and tickle the opponent's balls instead of punch them. Then the announcer says "MERCY".
If you do Cyrax's net enough times, he'll throw a laptop with the interNET on screen at you.
If you do Sub-Zero's freeze enough, he'll splash water on the opponent, then say "doh!" and shoot cold air to turn it into ice.
If you do Ermac's force lift enough times, he'll force push your screen away from the battle and onto the words "NOOB"
If you do Kabal's speed run enough times, after bumping into the opponent and causing him/her to spin, he'll say "Sorry gotta catch my train!"
J/K