The Furnace

Source coverage: 1 independent source, Miraheze The Furnace; checked 3 November 2026. Empty cells mean the referenced table does not supply that field.

No level and no elemental weakness are printed beside those hit points. A tier-list habit would invent a “bring blunt” line. I will not. What I can say about the aftermath is the Furnace Edge. On the weapons page, the second time that weapon breaks it becomes the Slagblade, and duct tape does not restore the edge. The fight is how the weapon enters the run. The tape rule is how it leaves.

Chainsaws, by contrast, do not break. They want gasoline. I mention that only so nobody tapes the Furnace Edge with a chainsaw habit. Different tools, different failure modes, both on the same weapons article.

The sewer page owns the entrance. This page owns the decision to fight. You can finish the game’s endings without this HP pool. That is what optional means here. It is not a story gate like the four offerings.

Cursed mode raises many enemies’ health by a range, not a single multiplier. I do not have a Furnace-specific cursed multiplier, so I will not apply the +25 to +50 band as if it were measured on this boss. The base row stands.

Iris keys are a different sewer-adjacent search. One iris key drops from the Furnace on the key article, and another copy exists in the Meat World. I note the drop because people hunting keys land on this fight by accident. The recommended iris route in that article is Hellride’s Lair in the parking garage, which can yield two before you ever boil this room.