I was experimenting around with my PS2 version of MUA, and somehow was able to use Moon Knight and Colossus without installing any mod!
Sometimes it works, and sometimes it doesn't.
How I did it:
-Load the simulator mission.
-Select Crimson Dynamo.
-When at the character select screen, remove all your heroes and don't replace them! Exit the selection screen.
-This should take you back to the simulator mission screen. Reselect Crimson Dynamo.
-Three heroes should be picked along with a fourth empty spot that says Moon Knight, or Colossus when you move your arrow over to it. MK is a more frequent appearance.
-Launch the mission, and both are playable.
NOTE: This has occurred very rarely to me.