The golem was a formidable foe, nearly impervious to conventional weapons, arrow fire, etc. But one day the golem was attacked by a strange worm that burrowed its way into the golem's energy core. The vast amounts of mana accelerated the parasite's growth until its tentacles burst from one side in a mass of wriggling appendages. It was strong enough to lift stone, allowing the golem to form a new "arm" of sorts. Indeed, now the golem could withstand blows AND rebuild itself. Frightening!