Fiery Plate Armor

Armor (plate), legendary (requires attunement)

While wearing this armor you are immune to fire damage and have a +5 bonus to your AC in addition to that provided by plate armor. As a reaction, when a creature enters an adjacent square or starts its turn next to you, you may command the armor to release a fiery burst. All creatures within 5 ft. of you must make a DC 15 Dexterity saving throw. Creatures who fail the saving throw take 6d6 fire damage while those that succeed take half this amount.