Suicune

Suicune's viability in ADV OU comes from its status as a bulky Water-type with Calm Mind, allowing it to check some of the tier's most dangerous physical threats while providing an offensive presence that other bulky Water-types lack. Defensively, Suicune's defenses outstrip Milotic's and Swampert's, giving it the heft to shrug off physical heavy hits and surprise special attacks from the tier's primary threats, Tyranitar, Salamence, and Metagross. Rest further bolsters its defensive prowess and boosting potential by giving it total recovery, making it much harder to stop. Combine that with Pressure, and Suicune's ability to PP stall special walls makes it a ticking time bomb. Offensively, Suicune's Calm Mind and natural bulk allow it to both dish out tons of damage and act as an emergency check to physical threats. Its offensive prowess is bolstered by its ability to run a variety of moves to work past potential counters, such as Ice Beam, Hidden Power Grass, Substitute, Roar, and Toxic. Suicune's versatility lies not only in its moves but also in its EVs, where modifications change the way Suicune is played altogether; RestTalk Suicune with offensive EVs becomes a potent early-game wallbreaker unlike defensive Rest Suicune's typical use as a late-game sweeper, while offensive Substitute sets with maximum HP are able to completely turn the tides against Blissey.

Suicune's most pressing flaw is its grounded status and pure Water typing, which render it vulnerable to Spikes and sand damage. Suicune's lack of recovery outside of Rest is also an issue—Suicune lacking Rest will be even more vulnerable to being worn down and will struggle to push through special walls like Blissey, but with Rest comes the danger that Suicune will be used as setup fodder by Spikes users and other sweepers while asleep. Suicune struggles to set up and sweep against teams containing an Electric-type or Celebi, the former of which threaten it with powerful STAB moves, while the latter resists its primary attack in Surf and can beat it with Leech Seed, Calm Mind, or the rare Perish Song to deny it safe setup and guarantee its KO if it's the last Pokemon standing. Suicune is also vulnerable to attackers wielding Self-Destruct or Explosion such as Metagross, Snorlax, Cloyster, and Gengar, which can KO it outright or weaken it to the point of uselessness. Suicune's lack of a resistance to Rock like Swampert or a recovery move without drawbacks like Milotic renders it vulnerable to being taken down by flinches in late-game scenarios against Dragon Dance Tyranitar and Choice Band Aerodactyl.