Marvel Super Heroes vs. Street Fighter/Moves

Armor Spider-Man
This grey version Spider-Man is based on a metallic suit he wore in the comics. His moves are identical to regular Spider-Man's, but he has Super Armor (which only functions while on the ground). However, Spidey's Super Armor only works against certain attacks (e.g. it will stop a Shield Slash, but not a Carbonadium Coil).

Mephisto
Mephisto is the father of Blackheart. Mephisto's moves are identical to his son's, but most of his regular physical attacks will set an enemy on fire, causing a minor amount of extra damage.

U.S. Agent
Although a distinctly different character than Captain America in the Marvel universe, he is just a palette swap in the game. While his moves are identical to Captain America's, he moves a little faster.