During game, hold down left and right buttons and hold left and right middle and ring fingers (it might take only one finger from each hand, but I use two) on the rear touch panel (it can be tricky), then enter the any of the following.

Code	Effect
left, left, right, right, up, down, up, down	Refills Health and Mana.
left, right, left, right, up, down, up, down	Attacks go through the Bard.
right, left, right, left, up, down, up, down	Bard is invulnerable.
up, down, up, down, left, right, left, right	Damage x 100.
up, up, down, down, left, right, left, right	Bard gets Adderstones and Silver Pieces.