The Golden Compass

This achievement is story related. Iorek will fight King Ragnar on the "Svalbard Courtyard" level and he is actually quite easy. Just get the button sequences right when you’re grappling with him and you’ll be able to attack (if you miss them you’ll have to defend). Follow the prompts for how to attack him - you can use high, medium, or low attacks or a slam.
As far as I can tell it doesn’t matter what you use. After a few grapple sequences you’ll take him down.

This may take a few tries but there is no reason for you to get mad.