Up, Up, Up, Left, Right, Left, + (Start) 100k (Team Menu)
Up, Up, Down, Down, Left, Left, Left, + (Start) All Character Code (Character Selection Screen)
Up, Down, Up, Down, Left, Right, Left, Right, Up, Down, + (Start) Unlock all costumes (Character Selection Screen)
left, left, right, right, up, down, up, down, + (Start) Unlocks Daredevil
down, left, left, up, right, up, down, left, + (Start) Unlocks Silver Surfer

Unlockable Heroes and Modes  -  There are a total of 7 playable characters which can be unlocked after performing certain ingame criteria.

Black Panther Collect Black Panther Action Figures throughout various acts
Blade Play Crane Game in Murder World
Daredevil Collect Daredevil Action Figures throughout various acts
Dr. Strange Rescue him from Mandrin in Act 1
Ghostrider Rescue him from Mephisto in Act 2
Hard Mode Complete the game on normal mode
Nick Fury Complete the game on easy or normal mode
Silver Surfer Complete all Comic Book Missions

Unlockables

Team Bonuses  -  Certain character combinations unlock special boosts.

Agents of SHIELD Captain America, Nick Fury, Spider-Woman, Wolverine
Agile Warriors : 10% Reduced Energy Cost Spider-Man, Spider-Woman, Elektra, Deadpool
Air Force Human Torch, Ms. Marvel, Storm, Thor
Alternate Identities Ironman - War Machine, Ghost Rider – Western, Spider-Woman - Secret Wars, Ms. Marvel – Ventura, Thor - Beta Ray
Bill
Assassins Blade, Deadpool, Elektra, Wolverine
Avengers : +5% damage Captain America, Thor, Iron Man, Spider-Woman, Ms. Marvel

Bad to the Bone Blade, Ghost Rider, Luke Cage, Wolverine
Bruisers : +15 Striking Thing, Captain America, Luke Cage, Ms. Marvel

Classic Avengers Black Panther, Captain America, Iron Man, Thor

Dark Past Blade, Elektra, Ghost Rider, Spider-Woman
Defenders Dr. Strange, Iceman, Luke Cage, Silver Surfer
Double Date Black Panther, Invisible Woman, Mr. Fantastic, Storm

Fantastic Four : 20 Health per KO Mr. Fantastic, Invisible Women, Human Torch, Thing
Femme Fatale : +5% Damage Ms. Marvel, Storm, Invisible Woman, Elektra, Spider-Woman
Flashback Iceman in Snowy Form, Captain America in WW2, Daredevil in Original, Ghost Rider in Original, Iron Man in Classic, Orig. Ms.

Marvel, Classic Wolverin
Martial Artists Black Panther, Captain America, Daredevil, Moon Knight, Nick Fury
Marvel Knights Black Panther, Daredevil, Dr. Strange, Luke Cage, Spider-Man, Moon Knight
Marvel Royalty Black Panther, Dr. Strange, Thor, Storm

Natural Forces : 5% Dmg inflicted as Health Gain Thor, Strom, Human Torch, Ice Man
Natural Leaders Captain America, Dr. Strange, Mr. Fantastic, Nick Fury, Storm
New Avengers : +5% All Resistances Captain America, Luke Cage, Wolverine, Spider-Man, Spider-Woman
New Fantastic Four Ghost Rider, Luke Cage, Spider-Man, Wolverine

Power Platoon : 20 Energy per KO Silver Surfer, Iron Man, Ms. Marvel, Thor

Raven Ultimates: +6 body,strike, and focus Deadpool, Colossus, Moon Knight, Thing

Scorchers Ghost Rider, Human Torch, Storm, Thor
Supernaturals Blade, Dr. Strange, Ghost Rider, Thor

Think Tanks: +15% Max Health Dr. Strange, Mr. Fantastic, Spider-Man, Iron Man

Weapons Specialists Blade, Captain America, Deadpool, Elektra, Nick Fury

X-Men Colossus, Iceman, Storm, Wolverine