Transform into Overlimit Chopper in Story Mode - In order to do this, you must have completed 2 previous tasks:

Defeat Overlimit Chopper in Story Mode - Create the Rumble Ball -
After achieving those requirements, you will now be eligible to transform into Overlimit Chopper. To do so, you first must be in a boss fight. While in the fight you have to use TWO Rumble Balls (wait for one to run out, heal SP gauge, take another one). While you are using the second Rumble Ball, the enemy has to kill Chopper. Instead of dying, like he normally would, a cinema scene occurs. The scene shows Chopper taking a third Rumble Ball and he transforms into his Overlimit form. He gains a new HP and SP bar. He isn't able to use items.

Unlock Survival Mode - In order to unlock Survival Mode, you must unlock the following characters in vs. mode. All characters MUST be defeated to unlock them. All locations given are the first location you encounter each enemy.

Effect - Code

Bazooka Marine - Defeat one in the Seaside Zone
Blue Demon General - Defeat one in the Cave Zone

Cluster Demon Soldier - Defeat one in the Cave Zone
Crimson Demon General - Defeat one in the Cave Zone

Knuckle Pirate - Defeat one in the Ruins Zone

Marine Corps Chief - Defeat one in the Jungle Zone

Normal Marine - Defeat one in the Seaside Zone

Pistol Pirate - Defeat one in the Jungle Zone

Sabre Pirate - Defeat one in the Jungle Zone
Sword Demon Soldier - Defeat one in the Cave Zone

World Government Agent - Defeat one in the Ruins Zone