Abomasnow

Mega Abomasnow's great Attack and Special Attack stats and powerful STAB attacks in Blizzard and Wood Hammer alongside coverage moves like Focus Blast and Earthquake make it an effective wallbreaker. Mega Abomasnow also enjoys switching into common walls in the tier like certain variants of Xatu, Vaporeon, and Seismitoad. Soundproof prior to Mega Evolution also helps the matchup against the likes of Heliolisk and Vikavolt by giving an immunity to what would otherwise be highly damaging STAB moves. However, a poor Speed stat and a vulnerability to entry hazard damage make it rather easy to wear down and revenge kill. Even Xatu and the Water-types it can supposedly switch into threaten it in one way or another, be it Toxic from Xatu or Vaporeon or Fire-type coverage from Slowking. Lastly, it faces competition with other breakers like Alolan Exeggutor and Mega Glalie that are overall faster and more powerful.