Ditto

Ditto is frankly a terrible Pokemon in Ubers; however, it holds a nanoscopic niche, as it can switch into paralyzed Mew that isn't attacking and threaten to transform into it, usually forcing it to switch out to a more passive teammate, such as Chansey or Mewtwo, dispelling any boosts it may have. It can also attempt to PP stall Mewtwo, Slowbro, and Chansey. However, it can't PP stall effectively because the first two are extremely hard to switch into once Ditto runs out of PP itself, and the latter 3HKOes Ditto with Seismic Toss due to its HP not changing after it's transformed. Ditto takes on the reduced Speed stat of the paralyzed Pokemon it's transforming into even if it isn't paralyzed itself. It also uses its own stats when landing or receiving a critical hit, making it extremely weak to them. Ditto is completely crippled by paralysis, and its niche of forcing Mew out is done far better by other Pokemon, such as Exeggutor, Zapdos, and Aerodactyl. Ditto doesn't do enough damage with any Amnesia boosts it may copy, and it doesn't have enough PP to stall adequately.