Arctic Biome Horse?

To my current knowledge, no. The Tundras seem to be a barren wasteland with treasures hidden about. No animals to speak of besides moose, wolf, bear, deer, fox, hare and penguins. Although I think moose should be rideable and penguins should be rideable on hills as a sled, no rideable animal exists yet but the mighty horse. Java had donkeys and camels to ride, so who knows what mounts they will add!

Nah, save the tundra for sled dog teams for the rustic or snowmobiles for the modern if those ever get added to the game. Having horses, donkeys, etc. where they don't belong would just be weird.

And yes anotomecally moose can be ridden, but they're also like 7 feet tall, you'd need a ladder to mount every time which again would look weird not to mention they are solitary creatures and not well domesticated.

wouldn't mind a rib able seahorse!