Certain character combinations unlock special boosts.

Boost	Combination
Agile Warriors: +2 all Attributes	Daredevil, Spider-Man, Deadpool, Iron Fist.
Bruisers: +5 Striking	Juggernaut, Hulk, Thing, Luke Cage, Thor.
Classic Avengers: +15% Max Stamina	Hulk, Thor, Iron Man, Captain America.
Fantastic Four: +35% Fusion Gain	Mr. Fantastic, Human Torch, Thing, Invisible Woman.
Femmes Fatales: +5% Damage	Jean Grey, Storm, Invisible Woman, Ms. Marvel.
Martial Artists: +5 Striking	Daredevil, Wolverine, Iron Fist, Deadpool.
Masters of Energy: +15% Max Health	Gambit, Iron Fist, Jean Grey, Ms. Marvel, Nick Fury, Penance.
Natural Forces: +5% Damage Inflicted as Health Gain	Storm, Iceman, Thor, Human Torch.
New Avengers: +10% to all resistances	Ms. Marvel, Spider-Man, Wolverine, Iron Man, Luke Cage, Iron Fist.
Pro-Reg Heroes: +15% Max HP	Iron Man, Mr. Fantastic, Deadpool, Songbird, Ms Marvel, Spider-Man.
Secret Avengers: +3 Teamwork	Captain America, Iron Fist, Luke Cage, Invisible Woman, Human Torch, Storm, Spider-man.
Shut Up Already: 15% Extra Health	Play as a team of Spider Man, Iceman, Deadpool, and Human Torch.
Think Tank: +15% Max HP	Mr. Fantastic, Iron Man, Green Goblin, Spider-man, Hulk.
Thunderbolts: +5% Damage	Green Goblin, Songbird, Venom, Penance.
Weapon Specialists: +5% Criticals	Daredevil, Deadpool, Gambit, Thor, Green Goblin, Captain America.
X-Men: +15% Max Stamina	Gambit, Jean Grey, Wolverine, Storm, Ice Man, Juggernaut (interchangeable).