ITT: We give our favorite Pokemon sidegrades. No strengthening or weakening them, but changing the way they work while keeping them just as viable.

No stat changes.

For Cloyster, I propose he become pure water type. He'll lose the STAB on his ice moves, making him less usable as a Shell Smasher, but he gains a much better defensive typing. Now, he can function as a defensive pivot instead of a set-up-and-sweep attacker. He can reliably spin away any hazards while setting hazards of your own thanks to losing his Stealth Rock weakness. He also gains a reason to run Overcoat, which got a nice buff this gen.

tl;dr - water type Forretress is best Forretress.