When you complete the following tasks the corresponding options will become available which will allow you to unlock different features in Battle mode.

Unlock Team Power Option:
Get 2 head shots in a row.

Unlock Custom Option:
Get a 100% hit head shot status twice in a row.

Humans and Creatures Option Method 1:
In Single-Player mode have a character on your team get their weapon fully upgraded.

Humans and Creatures Option Method 2:
In Single-Play mode have no characters miss during an entire level.

Unlock Defeat Leader Option:
Complete an episode with ALL the team members having 100% health.

During gameplay enter the following codes

Unlimited Turns
Press Up, Up, Down, Down, Left, Right, Left, Left, Right Trigger, Left Trigger.

Unlock Big Head Mode:
Press Up, Left, Down, Left, Down, Up, Up, Left.

Unlock Disco Mode:
Press Left Trigger, Left, Left Trigger, Left, Right Trigger, Right, Right Trigger, Right.

Unlock Low Gravity:
Press Up, Up ,Up, Up, Up, Up, Down, Right, Up.

Unlock Level Select:
Beat the game twice to unlock the 'Level Select' option