THEHAND ... Elektra swimsuit
REIKO ... Solara swimsuit
MONROE ... Storm swimsuit
SAVAGELAND ... Fantastic Four Comics
NZONE ... Tomorrow People comics

Brigade ... Beat him in Iron Man's third story stage.
Daredevil ... Beat him in Daredevil's third story stage.
Fault Zone ... Beat him in Storm's third story stage.
Hazmat ... Beat him in Magneto's third story stage.
Human Torch ... Beat him in Johnny Storms's third story stage.
Iron Man ... Beat Brigade in Iron Man's third story stage.
Magneto ... Beat Hazmat in Magneto's third story stage.
Niles Van Roekel ... Clear the Paragon fourth story stage.
Paragon ... Clear Paragon's third story stage.
Solara ... Beat her in Venom's third story stage.
Storm ... Beat Fault Zone in Storm's third story stage.
Venom ... Beat Solara in Venom's third story stage.

After clearing story mode with Spiderman, create a versus mode fight between Spiderman and a CPU Venom on the New York City Bridge. Win the fight and the arena should be unlocked.

Submitted by meefas In Versus Mode, play as Fault Zone against a CPU Storm in the NYC streets. Win and you will unlock the Bugle as well. Submitted by Metrexboy2

Create a Versus game and set the number of wins to one. After ten Versus matches, a new stage or character will be unlocked.

Submitted by Y2jhigga

Fight 160 versus mode matches. With handicaps on, this should be quick.

Alternate solution by morty