Now on to Frostburn...
Note that pretty much everything here belongs in the far north.
Branta - Sure.
Dire Polar Bear - Yup.
Megaloceros - These could actually be ok on the mainland, maybe.
Smilodon - Derp yes.
Wooly Mammoth - Yerp.
Domovoi - Yes, everywhere, including the mainland. One might come and live with a master smith or something.
Glacier Dwarf - I'm sure some dwarves live up north. They'd be the only ones with beards, though. In fact, they're probably closer to humans than dwarves, genetically.
Midgard Dwarf - I love these more than I can say. Maybe a couple of reclusive craftsmen of the frostlands, where brave heroes seek them out for their gifts of magical... stuff.
Elemental Weirds - North or on the Mainland, they're in either way.
Entombed - Yeah, sure. Even in parts of the Vallheim, they're probably good.
Frost Folk - Yes, as an evil sort of fey that hunts down people who try to make it across the Strait. Non-playable. Maybe when he strait freezes over they come south to hunt...
Genie, Qorrashi - Oh yeah, sure.
Frostfell Ghost - By now you should be able to tell that I'd say yes.
Frost Giant - Do I need to say anything?
Ice Golem - Yup.
Icegaunt - Uh-huh.
Marzanna - Oh goodness yes. I like this one.
Giant Raven - Yes. Raven Clan Wightspeakers can call these south to serve the Vallheim. Sometimes the choose to stay after they've been released.
Rusalka - Yeah, naked fey ladies are always solid.
Snow Spider - Ok, sure.
Spirit Animals - Can I get a resounding "hell yes"? I've been looking for something like this forever!
Tlalusk - I guess...?
Uldra - I'm always down for fey. They're in. Non-playable, though.
Vodyanoi - Yeah, why not? They're fine.
Winterspawn - Totes, dawg.
Yeti - Mmmmm... Yes.
Yuki-On-Na - Certainly!
Animals - Yeah, all of them, used reasonably.