Cresselia

Cresslia is a cornerstone of sun teams thanks to its recovery in Moonlight, an otherwise mediocre move, restoring much more HP. This, along with its excellent ability, Levitate, allows Cresselia to wall some of the most powerful Pokemon in OU, such as Garchomp, Dragonite, and Terrakion, which are troublesome Pokemon for sun teams. However, it's unable to threaten anything offensively due to its miserable offensive stats and lack of strong attacks. It's also more heavily pressured by Tyranitar than many other Pokemon due to its reliance on Moonlight for recovery and Tyranitar being able to Pursuit trap it easily. The issue of Moonlight's recovery is similarly crippling against rain teams, with rain teams also having brutally powerful Pokemon like Keldeo and Starmie able to 2HKO Cresselia.