Necrozma

With solid stats across the board backed up by Prism Armor, a lethal signature move in Photon Geyser, Calm Mind to boost its high Special Attack, and Heat Wave to nail Steel-types, Necrozma is a premier wallbreaker in RU. Its flagship set, the Calm Mind sweeper, is capable of punching large holes early-game and can blow past teams once its checks have been sufficiently dealt with. Necrozma is also capable of running an offensive Stealth Rock set that capitalizes on its great matchups against Donphan and every offensive Defogger in the tier, and it has methods of circumventing the entry hazard removers it can struggle against, such as Psychium Z for Mega Blastoise and Toxic for Mandibuzz. However, the Stealth Rock set faces competition from Metagross, which has a Steel / Psychic typing and an incredible physical movepool, and Nidoqueen, which can threaten a wider variety of Pokemon with its powerful STAB and coverage moves. Necrozma's base Speed of 79 is great, allowing it to get the jump on Mega Blastoise and Nidoqueen, but being unable to outspeed Drapion, Gardevoir, and Goodra can be problematic at times. Necrozma faces competition as a Psychic-type Calm Mind user with Sigilyph and Espeon, which can't be hit by Toxic, and Cresselia, which is weaker but far bulkier. However, Necrozma's great combination of power, bulk, and Speed make it more well-rounded than these options, so it is the primary choice for teams looking for a Psychic-type Calm Mind user.