Kreistor wrote:There's no hint that such a thing exists, and given it's potential overpower, I would suspect it would require an arkentool.
Magma golems or pet rocks?
Assuming you mean magma golems, the cost in time/materials needed could be a limiting factor in creating them. They could also have a disadvantage-style special ability that does damage to other units stacked with them. Or, perhaps, they would need to be exposed to heat every few turns or begin to cool (take unhealable damage, or decay as uncroaked).
Of course, this is all rampant speculation, but that's the best kind.