Quagsire

With its great defensive typing and fantastic ability in Unaware combined with decent physical bulk and access to reliable recovery, Quagsire has fashioned itself a clear niche in OU as a physical wall capable of taking on fearsome setup sweepers such as Belly Drum Azumarill, Mega Scizor, Mega Altaria, and Mega Charizard X. With Scald and Recover, it can stall out a good number of physical attackers in the tier, and a range of other move options means that it has very good defensive utility. Its Water / Ground typing gives it four resistances and an immunity to Electric, which, combined with its neutrality to Ice, makes it an excellent stop to momentum-grabbing Electric-types such as Raikou and Mega Manectric. It has only one weakness, but it is a 4x weakness to Grass, which means that it can be caught out by coverage moves such as Mega Metagross's Grass Knot. Additionally, while Quagsire can be very effective in a physically defensive role, its special bulk is somewhat lacking, and it can be 2HKOed by even relatively weak special moves. It also has underwhelming stats all-around, which prevent it from walling some of the most powerful physical attackers in the tier, and it is severely hindered by status ailments, as the chip damage from burn and poison can cripple it as an effective wall. Lastly, it faces competition from the other main Unaware user in OU, Clefable, as, while Quagsire checks physical threats more effectively, Clefable has better special bulk and can bring far more general utility to a team.