Choose Juggernaut, Iron Man, and BB Hood (in that order). Put them all on their recommended assist types. Get 3 Hyper Combo bars and link them all together (L=R). It should kill the opponent in one hit. This move was tested on Cable, a medium damage taker.
Choose Juggernaut, Incredible Hulk, and Zangeif. When at level 3, let Juggernaut be your active character, get very close, and press L + R to make them all do their hyper combos. This will instantly kill your opponent's character. Note: This attack best works when your opponent is in a corner.