317 Swalot

Infestation doesn't have good damage output, and is primarily used for its high energy generation, letting Swalot access its charge moves sooner. Rock Smash provides wide coverage as a Fighting-type move, but lacks STAB and has poor stats, especially with energy gains. 

Sludge Bomb costs the least amount of energy and benefits from STAB, making it Swalot's primary charge move. Ice Beam offers Ice-type coverage, which can be useful against Swalot's weakness to Ground-type Pokemon. Gunk Shot is typically not recommended due to its expensive energy cost, despite being the most powerful move available if unshielded. Acid Spray is mostly a gimmick to provide value when the opponent would shield a charge move, as it deals pitiful damage when not shielded which may lead to inconsistencies. 

Swalot is a mono-Poison type with high bulk and a moveset which largely emphasizes its charge move usage. Swalot's bulk is actually quite impressive, comparable to Tropius, making it the bulkiest among Poison-types in the meta while also having a niche with Ice-type coverage. Wins against all meta Grass Pokemon are to be expected (though some fights can be more messy than others), while resistance to Fighting-type damage is particularly valuable due to common usage of Pokemon with the fast move Counter. Unfortunately Swalot's moveset is a bit suboptimal due to the lack of low costing charge moves energy-wise, unimpressive fast move damage output, and overlapping coverage against Grass. Swalot has the stats to rise to the top, but a moveset update is needed to make that happen. 

Swalot lacks stats for Ultra League. 

One might accuse you of giving free wins if they see a Swalot in Master League. Maybe.