Lapras, Prioboss sounds like a cool concept. It does have one of the worst defensive stat groupings in the game, but at least it resists stealth rock. For its EV spread, I would do 252 Atk, 252 Spe, and 4 SpA / Def (depending on its moves), because putting 252 HP EVs on a Pokemon that has 20 base HP isn't going to do many favors.

Also, I wouldn't say that it covers Scizor, only because it can't hit Scizor super-effectively, and Scizor's Bullet Punch is going to do a lot to Prioboss, due to its bad defenses.

Also, do you want to list some more moves for it, and what it looks like? This way, we can get more of an idea of what Prioboss can do.