This was something I thought of when discussing what would happen to an iron golem in lava. I thought to myself, "What if an iron golem had a furnace in its chest, so it was constantly taking fire damage?"

Here's the result:

and here's the write-up for the background of the Furnace Golem, for those who are interested:

Furnace Golems

Born in the minds of madmen, the Furnace Golem is a nigh unstoppable engine of destruction. Where the Iron Golem can be used as a patient guardian, able to withstand the battering of time as surely as it can most everything else, the Furnace Golem is a fiery agent of destruction, an all-consuming conflagration encased within the near invincible frame of an Iron Golem.

The Furnace Golem was first created when Gizmo Grayling, artificer of renown, observed the Iron Golems ability to draw energy from flames to empower itself. Reasoning that, it being a construct of metal, it could be wrought into any shape before it was imbued with magical energies, Gizmo created what was possibly the most intricate Iron Golem of the age - its limbs were not solid but interlaced with vessels which led from the fingertips of his creation to its torso; a great, barrel-like chest housing a furnace repurposed from a blacksmith. When he completed his work, his creation stood before him - Its beautifully crafted and gilded limbs of steel, brass and copper standing at odds to the blackened iron of its chest.

When his creation was awakened, it functioned like any other iron golem, taking Gizmo's orders unquestioningly. Gizmo, ever thorough, ran a few tests with his Golem to determine its strength before he lit the furnace. The flames coursed through his creation, its chest glowing as the debris and grease in its limbs smoked from the heat. Gizmo went through the tests again, but even as the power of his creation grew, he saw in it a change - it was slower to follow his orders, and became increasingly prone to flashy feats of strength - throwing things it had been instructed to place down, destroying things it had been instructed to strike once. Too late, Gizmo tried to stop his creation - dousing it with water tanks he has prepared for the eventuality - but the Golem shielded itself from the torrents of water and escaped.

Ever since it escaped, the Golem has been on a single-minded spree of destruction. Consumed not only by an eternal hunger for fuel to keep its fire going but with an obsession with its own power, the Golem has disappeared into the wilds - trails of its destruction have been found - holes in the ground where trees have been torn up, but with the tree itself gone; Boulders thrown from the wild slopes of the mountains to create avalanches; and once, a dragon found dead on the borders of the mountains, its bones shattered and its heart ripped out. The Golem exists only to feed and to prove its strength, and so far has shown no greater aspirations than to keep its fire burning. Should it ever find its way back to civilization, there is no knowing how much destruction it could cause.

Gizmo, whose work had been undertaken in utter secrecy, denies everything, particularly when confronted by the blacksmith whose forge so recently went missing.

That was an amazing story.