Mamoswine

Mamoswine is a great pick for a Pokemon thanks to its good coverage, alright bulk backed by a decent Speed and great Attack, and the fact that it is one of the only viable Ice-types in the metagame. Mamoswine, however, is heavily walled by the two most common Rotom formes, Rotom-W and Rotom-H. Ice and Ground is also a pretty terrible defensive typing which allows a lot of common Pokemon in the metagame to check Mamoswine, such as Terrakion, Rotom-W, and Mega Metagross. Being very susceptible to Intimidate and burn doesn't help Mamoswine's case either. On the other hand, Mamoswine is very anti-meta because it checks a lot of common Pokemon, such as Heatran, Aegislash, Garchomp, Thundurus, and Landorus-T.