Extras become available upon the start of Adventure Plus. To access these "cheats" go to Special Features in the Main Menu.

10x Buff Duration(Battle Charge Lasts 10x Longer)
Big Head Mode.
Health Regeneration.
Little Head Mode.
Mana Cost(Spells use less)
Mana Regeneration.
One Hit Kills.
Regenerate Arrows.
Stone Skin(Take less damage from attacks)
Unlimited Arrows.