Archangel - can be found south of the X Mansion.
Beast - unlocked after completing story level 8 (Juggernauts and Crosses).
Colossus - can be found at the X Mansion.
Cyclops - unlocked after completing story level 7 (Bifrosty Reception).
Gambit - unlocked after completing the three Gambit events in the Manhattan Hub.
Havok - can be found south of the X Mansion towards the west coast.
Ice Man - unlocked after completing story level 8 (Juggernauts and Crosses).
Jean Grey - unlocked after completing story level 7 (Bifrosty Reception).
Polaris - unlocked after completing the bonus level The Thrill of the Chess (175 gold bricks).
Psylocke- Unlocked after completing 3 of her tasks around the city.
Professor Xavier - unlocked after completing his three events at the X Mansion.
Storm - unlocked after completing story level 8 (Juggernauts and Crosses).
Wolverine - unlocked after completing story level 4 (Rock Up at the Lock Up).