Fire Wolf Armor (5e Equipment)
From D&D Wiki
Armor (any medium or heavy armor), very rare (requires attunement)
Rumor has it that this armor was forged from the hide of a ferocious Guardian Wolf after it burned to death.
This magical armor grants a +2 bonus to your AC.
As a reaction when you are hit by an attack, you can speak the armor's command word, and it will ignite. The flames do no harm to you, but any creature that hits you with a melee attack or starts its turn within 5 feet of you takes 2d6 fire damage.