The Gamma Regulators, M'Kraan Fragments, and Asgardian Runes are located in the following spots. Collect five Gamma Regulators to unlock Hulk, five M'Kraan Fragments to unlock Jean Grey, and five Asgardian Runes to unlock Thor:

Act 1
Castle Doom - M'Kraan Fragment (1/10), Asgardian Rune (1/10)
Reactors - Gamma Regulator (1/10)
Missing Marvel - M'Kraan Fragment (2/10), Gamma Regulator (2/10)
Factory Floor - Asgardian Rune (2/10), Gamma Regulator (3/10), M'Kraan Fragment (3/10)
Capitol Offense - Gamma Regulator (4/10)
Underground Politics - M'Kraan Fragment (4/10)
Hallowed Ground - Gamma Regulator (5/10)

Act 2
Rebel Safe Harbor - Asgardian Rune (3/10), M'Kraan Fragment (5/10)
Push Back - Gamma Regulator (6/10)
Rooftops - Gamma Regulator (7/10)
Truckin' - M'Kraan Fragment (6/10)
Jacked Up - Asgardian Rune (4/10)
Cloaked - Asgardian Rune (5/10)

Register
Dock Work - M'Kraan Fragment (7/10)
Detour - Gamma Regulator (8/10)
Going Deep - Asgardian Rune (6/10)
Hit 'em High - Gamma Regulator (9/10)
Road Work - M'Kraan Fragment (8/10)
Traffic Jam - Asgardian Rune (7/10)
Containment - Asgardian Rune (8/10)

Act 3
Prison - M'Kraan Fragment (9/10)
Going Negative - Asgardian Rune (9/10), M'Kraan Fragment (10/10)
Tribal City - Gamma Regulator (10/10)
Panther's Lair - Asgardian Rune (10/10)