Mew

Mew is an extremely versatile Pokemon because it can learn every TM and HM in the game. Furthermore, Mew is the only Defogger in the metagame with access to Will-O-Wisp and no Stealth Rock weakness, which lets it cripple Defiant users such as Bisharp by halving their Attack. Overall, Mew has good offensive and defensive stats but is not really that outstanding when compared to bulkier Psychic-types such as Mega Slowbro, regular Slowbro, and Cresselia. Mew has a pretty good Speed stat as well, which lets it outspeed slower Pokemon and attack them. Mew also has access to a form of reliable recovery in Soft-Boiled, which contributes to Mew's longevity on the field. Synchronize is a useful ability for Mew, because it can punish status users if they inflict status on Mew. It can also provide utility against Scald burns. However, Mew's typing is subpar, which leaves it very vulnerable to common Bug-, Ghost-, and Dark-types, such as Scizor, Gengar, and Mega Gyarados. Mew also has four-moveslot syndrome because it cannot benefit from all move options it learns. Despite Mew's incredibly huge movepool, it only has a few viable sets that aren't outclassed by other Pokemon in the tier.