Storm Diver's Additions Mod/Enchanted Mushroom

The Enchanted Mushroom is a prehardmode accessory that is dropped from Angry Mushrooms. It initially grants 3 defense and 3% increased damage, but increases both by 3 for each quarter health the player loses, for a maximum of 12 defence and 12% increased damage when below 25% health.

Trivia

 * This accessory is unique in that the defense tooltip has "and increased damage percentage" added onto the end of it.