Guys, you shouldn't really be staying in on an Aegislash. For one, it has Shadow Ball. With Cloyster's (lowered) Special Defense you're probably gonna get KO'd in one shot. Observe:
252+ SpA Spooky Plate Aegislash-Shield Shadow Ball vs. -1 4 HP / 0 SpD Cloyster: 268-316 (110.7 - 130.5%) -- guaranteed OHKO - This is Aegis' most notable set on the ladder.
252+ SpA Spooky Plate Aegislash-Shield Shadow Ball vs. 4 HP / 0 SpD Cloyster: 178-211 (73.5 - 87.1%) -- guaranteed 2HKO - This is when you haven't set up yet.
Another thing, you can't give major hurt for the most part. Razor Shell hits 55% max; Hydro Pump less so. That alone lets you get hit to die. It doesn't matter whether you pack Hydro or Razor for Aegis. You still lose anyway. So yeah, if you want to sweep with this thing, you need a reliable answer for Aegis (and Steels in general).
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Ice Shard has its uses. One thing is you won't get picked off as easily by priority. Another thing is it's a good way to check fast dragons, although Mamoswine outclasses it in that job. In my opinion, coverage on Cloyster is not something to pass up.