Thanks guys!
Regarding amphibiousness: He does like water, but I can't see him wandering around on the sea bed (grendels don't like salt), so I'm not sure how well amphibian would fit.
As for reinvig etc: The real power of the guy is his full slots, which mean you can make up for any particular deficiencies like fatigueing. I don't think natural reinvig is necessarily thematic though, since it's a pretty rare thing in vanilla dominions.
Any ideas for alternatives to "claws"? And yes, he does hit like a truck! My first one got heroic strength, and rapidly reached strength 103! Smackdown!