Dark Pheonix Gauntletswondrous, very rare (requires attunement)

These black gauntlets have gold and feathered edging, with engraved motifs down their arms. While wearing them when you cast a spell that deals fire damage the flames flicker black instead of a bright orange and ignore resistance to fire damage. If these black flames reduce a creature to 0 hit points, it disintegrates into a pile of ash.

Additionally, when you are reduced to 0 hit points you instead burst into flame and appear to turn to ash. Until the beginning of your next turn you are paralyzed but are immune to all damage. At the beginning of your next turn you rise in a wreath of black flames with 1 hit point in an unoccupied space you can see. All creatures within 30 feet of this space must make a DC 18 Dexterity saving throw as they are engulfed in the inferno. On a failure they take 8d10 fire damage that ignores resistance, or half as much on a success.
After using this feature you can’t use it again for the next 2d6 days.

very rare