Heart of the Furnace is a Nightmare Unique relic, hunted from Cinder Wyrm once you are at Threat 20 or higher. It is one of four Exceptional drops on its list — 2.5% of the Uniques that boss gives up, about 1 in 40 — and every kill rolls the list twice. It is built on Eternal Cinderwake Relic — step 6 of the Cinderwake Relic line, item level 80 and up.

It always rolls the same numbers: +13% Ultimate Generation, +10 Power, +20% Fire Damage, +22% Burn Effect, +22% Ultimate Generation, +153% Fire Damage, +110% Ultimate Generation, +164% Burn Effect and +98% Power.

On top of that it carries Heart of the Furnace — Your Ultimate erupts 4 times over, every blast setting Burn and Igniting a full Burn, but your maximum health is 12% lower.

It fires Kindling Eye on its own: Every 5th critical strike ignites the target for 80% of the hit.

It leans into Burn.

It is Nightmare Gate loot.

Wearing it hands you Spirit Burst.

“The Wyrm's first coal, still refusing to be ash.”