A big black bear and a polar bear? Interesting! It reminds me somehow the two great bulls pretenders, which I personally love for their flavour.
The idea of an AoE paw which kills several men at once is very nice. The (mental) image of this great bear sending people fly around with its furious hits is epic - I think this Pretender would fit very well Marverni too. But aren't AoE attacks not influenced by strenght? This would be weird applied to the bear, as it is definitively its strenght to send people around...
P.S. nooo, please, no crown on a bear, noo, please. it stops being a king and becomes the dancing bear of the old gypsy circuses
if you really want to make him appear dominant, a giant alpha male, you could maybe consider giving him a mane of dishevelled, wild black hairs around his neck and shoulders (not as a lion but quite, you got the idea) Just my humble suggestion of course