To unlock Hard difficulty and Skrull Arena complete the game on Normal difficulty.
Unlockable Token Bonuses:
Unlock the following bonuses by obtaining the corresponding amount of tokens:
BONUS - TOKENS
Comic Covers I - 4 tokens
Comic Covers II - Get 4 tokens
Concept Art - 4 tokens
Fantastic Four (1990's) - 12 tokens
Fantastic Four (21st Century) - 12 tokens
Ultimate Costumes - 12 tokens
Filling the cosmic energy bar:
Do a taunt at any time. The taunt appears to do nothing, but it is actually filling a small part of your cosmic energy bar. The amount filled by each taunt varies. Note: It is recommended that this is done when there are no enemies around.