When you complete the game on the 'Normal' difficulty setting the following PSP exclusive modes become unlocked.

Hardcore Squad Mode:
(In this mode your initial team selection is fixed for the whole game and when heroes have been killed they cannot be revived. You can import 'Save' data to boost initial stats)
Complete the game once on Normal difficulty setting.

Hardcore Heroes Mode:
(In this mode Heroes that have been killed cannot be revived and you can import 'Save' data to boost initial stats)
Complete the game once on Normal difficulty setting.

Uber Hero Mode:
(Play with a single hero has his level raised to 99 and ALL powers and outfits maxed)
Complete the game once on Normal difficulty setting.

When your team consists of certain character combinations the indicated special boosts becomes unlocked.

Agile Warriors - 10% Reduced Energy Cost:
Spider-Man, Elektra, Black Panther, Ronin, Deadpool, Daredevil.

Femme Fatale - +5% Damage:
Storm, Ms. Marvel, Black Widow, Invisible Woman, Elektra, Spider-Woman, Ronin.

Agents of S.H.I.E.L.D. - +5 All Resistances:
Captain America, Wolverine, Black Widow, Nick Fury, Spider-Woman.

Weapon Specialists - +5% Criticals:
Captain America, Nick Fury, Black Widow, Deadpool, Elektra.

Classic Avengers - +15% Max Energy:
Captain America, Black Panther, Thor, Iron Man.

Avengers - +5% Damage:
Spider-Woman, Captain America, Thor, Iron Man, Ms. Marvel.

New Avengers - +5% - All Resistances:
Captain America, Luke Cage, Wolverine, Spider-Man, Spider-Woman.

Femme Fatale - +5% Damage:
Ms. Marvel, Storm, Invisible Woman, Elektra, Spider-Woman.

New Avengers - +5% All Resistances:
Spider-Woman, Captain America, Iron Man, Luke Cage, Spider-Man.

Assassins: +60% S.H.I.E.L.D. Credit Drops:
Black Widow, Elektra, Wolverine, Ronin, Blade, Deadpool.

Assassins - +60% S.H.I.E.L.D. Credit Drops:
Deadpool, Ronin, Wolverine, Blade.

Agile Warriors - 10% Reduced Energy Cost:
Elektra, Spider-Man, Spider-Woman, Deadpool.

Fantastic Four - 20 Health per KO:
Mr. Fantastic, Invisible Women, Human Torch, Thing.

Natural Forces - 5% Dmg Inflicted as Health Gain:
Thor, Strom, Human Torch, Ice Man.

Natural Leaders - +5% Experience:
Captain America, Storm, Mr Fantastic, Nick Fury.

New Fantastic Four - +15% Max Energy:
Ghost Rider, Spider-Man, Luke Cage, Wolverine.

Super Natural - +5% Health Reneneration:
Blade, Thor, Ghost Rider, Doctor Strange.

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

Bruisers - +15 Striking:
Thing, Captain America, Luke Cage, Ms. Marvel.

Air Force - +15% Max Health:
Human Torch, Storm, Thor, Ms. Marvel.

If you want to unlock your characters alternate costumes then complete the following tasks.

Unlock 2nd Costume:
Defeat 30 enemies.

Unlock 3rd Costume:
Defeat 175 enemies.

Unlock 4th Costume:
Beat the characters comic book mission.

Complete the following tasks to unlock the corresponding effects. There are seven playable characters that can be unlocked.

Unlock Hard Mode:
On Easy or Normal mode complete the game

Unlock Nick Fury:
On Easy or Normal mode complete the game

Unlock Silver Surfer:
Defeat Galactus

Unlock Dr. Strange:
In Act 1 rescue him from Mandrin

Unlock Ghost Rider:
In Act 2 rescue him from Mephisto

Unlock Black Panther:
Collect Black Panther Action Figures throughout the game

Unlock Daredevil:
Collect Daredevil Action Figures throughout the game