If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
In Marvel-vs-DC you play the role of X-men (Marvel) characters and fight against the Justice League (DC) characters. Choose from Wolverine, Cyclops, Gambit, or Psylocke and start fighting against the DC characters (Aqua man, Batman, and Wonder Woman).
Left / Right Arrow Keys - Move.
Up Arrow Key - Jump.
Down Arrow Key - Duck.
S, D - Attack.