Swampert

Mega Swampert is a very niche rain attacker. It's the only viable physical Swift Swim attacker, as well as the only one that can reliably beat Thundurus, Sylveon, and, depending on its coverage, Ferrothorn. Its immunity to paralysis due to its Ground typing means its Speed cannot be crippled like the others'. Also, as a rain sweeper with good natural bulk, it is less weak to priority moves than other rain sweepers, notably Talonflame's Brave Bird and Mega Kangaskhan's Sucker Punch. However, being a physical attacker, Swampert is hindered by Intimidate and burns, and it is extremely weak to Grass-types, more so than other rain staples. Unlike other Swift Swimmers, it needs to Mega Evolve before it gains Swift Swim, usually giving your opponent a free turn. Finally, its secondary STAB move Earthquake is significantly weaker due to its spread reduction, and it also hits Mega Swampert's partner.

Aside from its Mega forme, Swampert is also able to find a small niche due to its access to Wide Guard and great anti-meta coverage that allows it to take advantage of the users of spread moves that are stopped by Wide Guard, including Landorus-T, Mega Diancie, Volcanion, and Heatran. Additionally, it matches up quite well against common threats such as Talonflame, Thundurus, Jirachi, and Aegislash. Its bulk is well complemented by a strong defensive typing, making up for Swampert's low Speed that forces it to move last or close to it most turns. Like its Mega counterpart, base Swampert suffers from a lot of competition in its role on teams, primarily from Gastrodon, which offers a reliable form of recovery and a better ability in Storm Drain. Aside from Gastrodon, other bulky Water-types like Suicune and Wide Guard users such as Aegislash and Conkeldurr often fill Swampert's role on teams better than Swampert can. Although its coverage is nothing to be scoffed at, Swampert's Special Attack stat is far from impressive, leaving its attacks quite weak against resisted or neutral targets.