It'd be a gem if it were authentic, but unfortunately it isn't, considering what I see. Single inscribed balls are hard to come by, one with 4 inscriptions is unheard of, I'd steer clear.
I guess I would classify myself as a low-intermediate Mantle autograph person. However, one thing that jumps out at me is the large spacing between "Mickey" and "Mantle". As our friends the Brits like to say, "Mind the gap". Because you might fall flat on your face with this one!