Regirock

Incredible mixed bulk alongside its Rock typing means Regirock can serve as a premier Normal-, Flying-, and Fire-type check. Regirock also has access to an expansive support movepool with status options such as Thunder Wave and Toxic, which make it very difficult for offensive Pokemon to set up on it; entry hazards in Stealth Rock; and even weather moves in Sunny Day. From a defensive standpoint, mono-Rock typing allows Regirock to serve as a more reliable check to Fire-and Normal-types such as Pyroar and Tauros than Pokemon such as Rhydon, as common Water and Grass coverage moves are only 2x super effective rather than 4x. Unfortunately, Regirock relies solely on Leftovers for recovery, making it very vulnerable to getting worn down throughout a battle. Regirock also faces competition from Rhydon and Steelix, as both are similarly capable Stealth Rock setters, also provide solid Normal and Flying resistances, and have other niches, such as Steelix checking Psychic-types and Rhydon having a potent dual STAB combination and higher Attack.