Frumious Frock

Wondrous item, very rare (requires attunement)

The frumious frock is made of sleek tawny fur that radiates heat. You gain resistance to fire damage. When you are reduced to half of your maximum hit point total, you are overcome by a wild fey influenced fury for 5 rounds. During this fury, the frumious frock bursts into flames and hundreds of barbed quills emerge, with dozens of these quills twisting together into a viciously barbed tail. You gain the benefits of haste as well as a tail melee attack that deals 1d10 points of piercing damage and 2d6 points of fire damage (the tail attack has the finesse trait). While in this fury, your resistance to fire becomes immunity to fire damage. Any creature starting their turn adjacent to you during your fury takes 1d6 fire damage. Once the duration of the fury elapses, you gain a level of exhaustion. Unlike a creature using rage, you can cast spells or perform other actions requiring concentration while in a fury. You can enter the fury once, and regain the ability to do so after a long rest.