Omastar

Omastar has a really good matchup against fat teams, OHKOing almost half of the tier at +2 (Clefairy, Hitmonchan, and Eelectross drop to Waterium Z, while a little chip is required to snag the OHKOs on Type: Null and (Non AV) Lanturn. The fact that it can take advantage of mons like scarfed Scyther, Spritomb, Kangakhan, and Pyroar locked into fire blast is also amazing. A weakness to Priroity + being outsped by scarfers like Todemaru and Primeape, holds it back, but I think that Omastar is a very scary threat that is best represented in A.
While other shell smashers like Carracosta aren't as threatened by choice scarfers like Togedemaru and Primeape, thanks to its natural bulk. Omastar has a much better speed tier, overall breaking power, and arguably better coverage to hit its defensive checks.