I have a competitive cloyster, but I don't know what item to put on it.
Just in case it helps, it's moves are
Also its ability is skill link with EVS in attack and speed. Thanks in advance
I'd personally put a focus sash on cloyster because when you shell smash you're open to be hit by any attack and although cloyster has outstanding defense, it's special defense isn't as remarkable plus it's already lowerd by the shell smash. Focus sash makes sure the cloyster doesn't get KOd and then you can proceed to sweep the opposing team.