In secret, Yarin poisoned Highthane Gudrun Anvilmar and then arranged a rescue mission for his son, the lost Relgast Anvilmar, that brought him to the raptor city of Cary'leh, though this was a deception used to secretly poison Relgast as well.
When Skirvar reneged on his alliance with Javali at Fenris Isle, Ironforge was vulnerable. A coup occurred with Voutgar Blackhammer taking control and Yarin leading dwarves to support Javali in Hesperia. Skirvar was also in the region, and with help from agents of Ravenholdt he slipped into the dwarves' ranks.
When confronted by Skirvar, Yarin, in a true super-villain moment, proudly announced his betrayal and that he was the one responsible for poisoning both the Highthane and his heir. He then attempted to kill Skirvar as well, shooting at him with his boomstick. Urkath Oilfist intervened, taking the bullet meant for Skirvar and dying in the process. Percy Fayette leapt up to attempt to negotiate a peace and prevent the dwarves in attendance from erupting into violence, though it was only a diversionary tactic to obscure Yarin’s view of the furious Skirvar, who was standing behind the rogue during his speech… and channeling an enormous pyroblast! The fiery bolt erupted from the Dark Iron Thane’s hand and reached its target. The head and upper torso of Yarin were reduced to naught but ash and bone. The half-skeletonized corpse fell to the ground, and Skirvar turned to the crowd. With a booming voice, he addressed them - resolving the situation peacefully and returning them to Ironforge.
"I poisoned the Highthane. I poisoned his heir, Relgast, at Cary'leh. An' I'd poison ye too, Skirvar, 'xcept this gun is gonna do a cleaner job this time.