Hello there! I registered here just so I could throw my weight behind those asking for a Tarquin bug fix. I've had him not show up for the boat as well as not show up outside the graveyard. I play co-op and I've never actually been able to get Tarquin to make the anathema. I even resorted to reading how others obtained it and I was always unable to emulate their success.
Tarquin will make you the Anathema when you reach the city of Arx and after finding a book/letter in the white magisters barracks that implicates Tarquin in the direct revival of Braccus Rex. Hope this helps.
