According to showrunner D.B. Weiss, the masterminds behind TV's most popular show had been lobbying to include a zombie polar bear in an episode for the last four seasons (go figure). "What we had to do to get the zombie polar bear, was writing the zombie polar bear into every season of the show for about four seasons," said Weiss. It's an outlandish concept to be sure, so Weiss further explained that the idea was initially met with resistance, as the special effects crew said year after year: "'Fuck you, we cannot afford a zombie polar bear.'"
Lo and behold, the funds were allocated, and what we got was absolute bastard of an animal. Director Alan Taylor told Entertainment Weekly that the bear was designed by the New Zealand-based design and effects company WETA. And as evidenced by the video, an actor wearing a green suit was lucky enough to play the animal's part, while its victims were flung into the air with the aid of wires and, yes, more green screens.