Thor's Mjolnir's Might or Dare Devil's ES seem perfect for this and only get better as you quickly level.

If your heroes are capable of quickly killing (one or two attacks) these low HP mobs, you will rapidly level all of your heroes or get costumes of heroes you don't already have. The demons respawn so quickly, that throwing attacks that return (Thor's hammer throw, DD's Extensive Strike for example) can actually kill one on the way out and one on the way back. This is the fastest respawn rate that I've run across in the game (much faster than the Omega Base simulation missions' infinite spawn room or the Asgard simulation area). Where the demons spawn, they will instantly respawn after every death.

In Mephisto's Realm in the beginning area with the alter that reads, 'Thy way shall be lit by the flames of impure souls.' you can garner huge amounts of XP (infinite, if you wish) in a very short amount of time. down, left, left, up, right, up, down, left Infinite Experience.left, left, right, right, up, down, up, down - Unlock Daredevil.up, down, left, right, left, right, start - Unlock all skins (in the Team Menu).Left, Right, Left, Right, Up, Down, Up, Down, Left, Right, Start - Unlock all powers (at the Character Selection screen).Up, down, right, left, up, up, down, start - Unlock all Load Screens (Review Menu).Up, Down, Up, Down, Left, Right, Left, Right, Up, Down, Start - Unlock all costumes (Character Selection Screen).Left, Right, Down, Down, Right, Left - Touch of Death (In-game).Up, Right, Left, Down, Up, Right, Left, Down - The Courses (Comic Book Mission).Up, Left, Up, Right, Down, Right - Super Speed (In-game).Up, Left, Up, Left, Down, Right, Down, Right - Level 99 (Team Menu).Up, Down, Up, Down, Up, Left, Down, Right - God Mode (In-game).Left, Right, Right, Left, Up, Down, Down, Up - Filler (In-game).

Up Down, Right, Left, Up, Up, Down - All Wallpapers (Review Menu).

Down, Down, Down, Right, Right, Left, Down - All Concept Art (in the Review Menu).

Left, Right, Right, Left, Up Up, Right - All Comics (in the Review Menu).

Up, Left, Left, Up, Right, Right, Up - All Cinematics (in the Review Menu).

Up, Up, Down, Down, Left, Left, Left, Start - Unlock All Characters (at the Character Selection Screen).

Up, Up, Up, Left, Right, Left, start - 100k (in the Team Menu).

Note: You will no longer gain Achievement Points after you enter these codes (with the exception of the Daredevil and Silver Surfer codes). Some codes require repetition, and others require a press of Start after the code chime rings out. Enter this codes quickly at the time indicated below.

Marvel ultimate alliance cheat codes