Hes hairy with black pincers, so probably not good! Its a mythrax or xanthid crab of some sort probably a gorilla crab. Ditch it or toss it in the sump IMO.
Freaky looking. IMO crabs are bad. I took a chance with a xanthid crab before. He did good for about 6 months then every snail, and shrimp in my tank along with a fish came up missing over about a months time. I took him out and never had a problem after that.