Celesteela

Celesteela is a very potent wall in AG, capable of checking common Pokemon such as Swords Dance Ultra Necrozma, Necrozma-DM, Arceus-Fairy, Arceus-Ground, Arceus-Steel, Extreme Killer Arceus, and non-V-create Mega Rayquaza. Its high viability comes from its ability to check almost all Arceus formes and Pokemon that struggle to deal significant damage to it due to its ability to easily recover HP while simultaneously wearing down the opponent's team with Leftovers, Toxic, and Leech Seed. Furthermore, Celesteela possesses a stellar Steel / Flying typing as well as phenomenal natural bulk to go along with it. Immunity to the omnipresent Toxic makes it far easier for it to take on bulky support Pokemon that rely on poisoning the foe, making Celesteela much more challenging to break. Due to how passive it is, however, it's able to be trapped and removed by Shadow Tag Pokemon such as Gothitelle and Will-O-Wisp Mega Gengar, leaving the team open to being annoyed by the offensive and bulky Pokemon that Celesteela handles. Also, Pokemon such as Mega Rayquaza, Extreme Killer Arceus, and Swords Dance Arceus-Ground commonly carry moves to beat Celesteela, with the former carrying V-create and the latter two carrying Substitute in order to set up and take out Celesteela one-on-one. Lastly, due to Celesteela's passive nature and method of removing opposing Pokemon, it cannot properly take advantage of Beast Boost.