(Arcade, Genesis, SNES; 1991):
1-4 players (As usual, characters are forced on the coin slots in 4 player mode, and selectable in 2 player mode)
Button 1: Attack/Pick up objects/Throw objects
Button 2: Jump
Genesis controls(adjustable in the options):
B/C: Attack/Pick up objects/Throw objects
SNES Controls (adjustable in the options):
Y: Attack/Pick up objects/Throw objects
A: Projectile attack
As you can see, the Genesis version doesn't use it's 3rd button as wisely as the SNES version does. Because of both differences in controls, I'll explain the rest of this in arcade controls. It shouldn't be hard to translate to the console of choice.
Hold 1 for a few seconds to guard(The SNES version seems to lose the ability to do so), which still leaves you vulnerable from behind. If you press 1 when you're extremely close, you'll lift an enemy over your head, where you can throw, or jump and throw. 2, 1 jump attacks, which differs from the high and low point of the jump. 1 & 2 simultaneously will perform a projectile attack(with the SNES having a single button for this, default being A), which is the most powerful attack the player has, and can be done during jumping. Healing items, usually dropped by cameo Avengers appearances, are picked up automatically, by walking over them.
There are shoot 'em up sections every so often, in which either button fires.
In 2 player arcade mode, you can add to your health, which is represented by numbers, by pressing Start, if you put in enough coins to have enough credit to do so. In 4 player mode, you actually start the game on the character select screen, by pressing the attack button of the controls of the character you want to play as, so you lose the ability to add health like this.
The Genesis version came out pretty ugly, due to poor color selection by Opera House, so this patch makes it's coloring much closer to the arcade version, and even brings out details that were hidden with the shoddy coloring: http://www.romhacking.net/hacks/2283/