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 (L1=R1). This should kill just about any opponent with one hit. This move was tested on Cable, a medium damage taker.

Choose Juggernaut, Incredible Hulk, and Zangeifet. Let Juggernaut be your active character when you reach level 3, get very close, and press L1 + R1 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.