Smeargle

Smeargle has access to virtually every move, which makes it the only viable Smash Pass Pokemon in Ubers due to its access to both Spore and Shell Smash. It is important to note that Mega Diancie, which looks like a full stop to passing successfully due to its immunity to Spore and ability to OHKO most recipients, falls to a +2 Hidden Power Steel. Smeargle's poor bulk makes it especially susceptible to priority attacks. It also struggles versus common Pokemon such as Darkrai, Mega Sableye, Substitute Perish Song Mega Gengar, and Pokemon with Lum Berry, especially Lum Berry Tyranitar. Finally, using Smeargle requires experience and usually involves a risky game of predictions, and it can only be used once each game.