He's killed living beings before but Genndy has said several times that he's never killed a human before. That's the specific issue with him killing one of the daughters that Genndy said this season would dwell on. Also he didn't kill the Viking, he freed him from the curse and he aged rapidly and died of old age. If anything he mercy killed him which is kinda different, I guess. Tooooo be fair it's actually sampling it, not just an "ode" to it, haha. He's been in a few ads already, and Genndy said he and the Guardian would show up.