Slowbro

Mega Slowbro is one of the most consistent setup stall Pokemon in the 1v1 metagame. With naturally monstrous Defense, it can tank neutral attacks from the strongest physical attackers in the tier, such as Mega Charizard X, Flyinium Z-boosted Fly Dragonite, and Mega Lopunny, even without Defense investment. Thanks to this, Mega Slowbro can put as many EVs into Special Defense and HP as possible, which enables it to tank moves from powerful special attackers as well, such as specially offensive Dragonite and Choice Scarf Porygon Z, and follow up with recovery in the form of Slack Off or Rest, or use various setup moves such as Iron Defense, Calm Mind, and Amnesia in order to get out of KO range. Slowbro also has access to two very useful abilities for its role, those being Oblivious and Shell Armor, allowing it to be immune to the move Taunt, which normally shuts down all forms of stall, before Mega Evolving and avoid being hit by a critical hit after, making it more reliable against every Pokemon that can boost its offenses. Mega Slowbro is, unfortunately, one of the slowest Pokemon in the metagame, so it is only able to set up after it has already taken damage, leaving it susceptible to being knocked out by sufficiently powerful super effective attacks. Mega Slowbro is also weak to several common attacking moves, those being Grass-, Electric-, and Dark-type moves, so you'll need to watch out for moves such as Giga Drain, Thunderbolt, Dark Pulse, and their respective Z-Moves from Pokemon such as Mega Venusaur, Magnezone, and Hoopa-U.