I have a minor suggestion. The Ice Relic currently has no effect outside of combat, but it would be neat if it froze water. It could also maybe create a layer of snow when used on more solid blocks. I was impressed by the geomancy item, especially by the fact that you can stand on the larger boulders and ride them, so I figured more little details like that would be nice.
Other than that, I just have to say that you've done an amazing job, and that this is shaping up to be one of the best mob mods out there. When I saw the Frostmaw in the planned mob section a few months ago, I never imagined it would be as spectacular and awe inspiring as it was when I first encountered it. Other people have already suggested how to fix his weakness to ranged attacks, so I really have nothing to offer other than to say good job. The detail put into the monster's roar is particularly awesome.