Swampert

As the premier answer to some of the tier's most feared physical attackers and offense in general, Swampert is truly a leviathan of ADV OU. Defensively, Swampert's solid bulk and resistances to Rock and Steel allow it to answer Tyranitar, Metagross, and Aerodactyl; its access to Ice Beam allows it to counter physical Salamence and Flygon; and its immunity to Electric allows it to stop Electric-types like Zapdos and Jolteon that run Hidden Power Ice. Furthermore, Swampert's immunity to sand and access to Refresh and Roar give it both longevity and the ability to check setup sweepers on balanced and defensive teams, especially in conjunction with Protect to scout offensive Pokemon and gain passive healing from Leftovers. Swampert's defensive prominence is such that it has encouraged both Electric-types and mixed attackers to run Hidden Power Grass as a standard move for the sole purpose of beating it, a testament to its ubiquity and value. Offensively, Swampert's durability and solid Special Attack, as well as Torrent, give it the ability to fire off strong Hydro Pumps at defensive cores, and it can wield Earthquake and Focus Punch to dismantle Blissey, the tier's answer to special moves. Swampert can also run a Substitute + Endeavor set, whose potent Hydro Pump and immunity to sand make it a threatening wallbreaker or cleaner. On offensive sets, the characteristics that make Swampert's defense so stifling can be used to develop momentum and exploit mismatches and free turns with ease. Despite all this, Swampert struggles to break through the tier's other bulky Water-types, Milotic and Suicune, and it is walled cold by Celebi, which can outright use it as setup fodder. Furthermore, Spikes and attackers running Hidden Power Grass threaten to take huge chunks out of Swampert's HP, and its lack of recovery outside of Leftovers can make it difficult for it to last throughout a game.