Uxie

Although Uxie is mostly overlooked in favor of its bulkier Psychic-type cousin Cresselia, it can act as a useful pivot and Stealth Rock user, which is enough to earn a niche. Its enormous supportive movepool, which features Yawn, U-turn, Memento, Knock Off, and Thunder Wave, makes it a very versatile Pokemon that can freely choose moves and EV spreads to accommodate its team's weaknesses. A high Speed stat for a defensive Pokemon allows it to potentially outspeed several threats to beat them with ease, such as Toxicroak, Roserade, and Nidoqueen. Uxie fits on offensive and bulky offensive teams that need a Fighting- and Poison-type counter that can avoid passivity issues, unlike Cresselia. Its ability to facilitate setup from the likes of Barbaracle and Slurpuff also makes it a great pick on these archetypes. Its great ability in Levitate can let it switch into dangerous Ground-types like Flygon and Nidoqueen. It also has a great matchup against opposing offensive teams, as it is able to quickly disrupt their momentum with Yawn and U-turn. However, despite having Yawn and U-turn to combat its passivity, Uxie's mediocre and uninvested Special Attack means its attacks are still very weak, which is an issue against Pokemon that don't mind being put to sleep, like Snorlax and Calm Mind Cresselia. Although base 130 / 130 defenses are amazing, they are let down by its slightly mediocre HP stat. This makes it more vulnerable to moves such as Pursuit compared to Cresselia. Most importantly, however, despite its extensive movepool, Uxie has no way to reliably recover its HP. This makes it very hard to consistently check the threats it's supposed to throughout the entire match. Although Wiki Berry slightly alleviates this, it makes Uxie much more inconsistent on bulkier teams, where Cresselia is preferred and its passivity can be accommodated.