Use of the Rabbit Ears Chalice
If you do Roger's Ancient Book Sidequest, you'll eventually uncover an item called the Rabbit Ears Chalice in the Ursa Lava Caves. With the item equipped, enter the code below during a battle to have that character blow up and deal damage to the enemy.
Code - Effect
Up, Up, Down, Down, Left, Right, Left, Right, (Circle X or X Circle, depends on refinement) - Character explodes and deals damage.