Cresselia

Cresselia's incredible 120 / 120 / 130 bulk, ability in Levitate, and access to reliable recovery turn it into one of the most threatening defensive Pokemon in the tier, capable of checking devastating Pokemon like Salazzle, Dragalge, and Virizion. A reasonably good base Speed stat of 85 lets Cresselia outpace and OHKO Pokemon like Pangoro with a bit of Speed investment. Its amazing support movepool with options like Thunder Wave, Toxic, and Lunar Dance allows Cresselia to support its teammates well. However, Cresselia is commonly labelled as a "do-nothing" Pokemon, and for good reason. Its lackluster Special Attack and lack of any way to beat opposing walls other than Toxic will leave it helpless against other balance staples like Registeel and stallbreaker Mandibuzz. Cresselia's mediocre defensive typing means that it'll only be resisting a couple of attacking types while losing to a plethora of Bug-, Dark-, and Ghost-types. Moonlight's limited PP will quickly leave Cresselia struggling to switch into attackers like Dragalge. Cresselia also has a massive vulnerability to status, notably Toxic poison and paralysis. For example, if Cresselia has been inflicted with Toxic poison, it'll struggle to consistently switch into Pokemon like Shaymin, Salazzle, and Roserade. In the same way, once Cresselia is paralyzed, it will no longer be able to outpace and check Pokemon like Bewear and Pangoro.