Thoughts: Hippowdon is a really good Pokemon, thanks to its bulk and the chip damage it provides. SR and Toxic is something that a lot of Pokemon have, but Sand Storm pushes it to another level and Hippowdon is able to beat most Pokemon that are immune to it. Its phyiscal bulk helps it against many physical threats in the metagame.
Checks: Grass- and Water-types do really well against it. Tapu Bulu has to be careful because of Toxic, but it remains healthy with its Terrain and Horn Leech. Zarude and Tapu Fini don't care about status and they both stay healthy with either Draining Kiss or Jungle Healing. Zarude abuses Hippowdon for easy set-up and Fini does that or it removes its hazards.
