Select the Anti-side and then talk to Goliath before going to 'Missions' and he'll tell you which heroes you will be able to recruit as playable characters by completing a certain task.
Score 15,000 points within a time limit.
Score 25,000 points or higher while standing in Thor's way.
Score 30,000 points or higher, protect him and the civilians and defeat Scorcher in his bonus mission.
Unlock Green Goblin:
Set the charges within the time limit and score 30,000 points on his bonus mission.
Unlock Jean Grey:
Score 13,000 points or higher, destroy ALL targets with exploding robots and defeat Grey Gargoyle in her bonus mission.
Unlock The Thing:
Score 15,000 points or higher, defeat the Lizard and ALL other enemies in under 9 minutes on his bonus mission.
Score 30,000 points or higher, collect as many data discs as possible and defeat as many enemies as possible. Then go to the exit in his bonus mission.
Lead the scientists to safety and earn over 15,000 points in her bonus mission.
Defeat over 75 enemies, Scorpion, and earn over 25,000 points while keeping Penance alive.
Save Venom and get 25,000 points on his bonus mission.
Added by: Sanzano Sep 22nd 2009, ID#32331