The Furnace is a Rare card that is unlocked from the Hog Mountain (Arena 10). It is a moderate-hitpoint building that spawns a Fire Spirit every 6 seconds and spawns one Fire Spirit upon destruction. It appears to be a cast-iron steam train furnace with a bubbling cauldron holding magenta fluid resembling Elixir on top of it. It is also covered with various other props, including a ladder on the side of it, and a pile of firewood on the other. A Furnace card costs 4 Elixir to deploy.