Polar bears are a custom creature added on Otherlands.
They are somewhat stronger in combat than normal brown/black bears, and they are faster as mounts or when dragging carts.
You can get them initially by feeding Enchanted Frost Berries to a brown/black bear, the berries are a present from 2023 xmas gift.
To convert a bear – activate a frost berry and use “Offer” action to a bear. For this to work you shouldn’t be in combat with it.
Polar Bears require taming to lead/ride unless you have 50 Animal Husbandry and Animal Taming.
They can be tamed/dominated as normal, and they can be bred like any other animal.