I'd like to nominate Alolan Muk. It's kind of a one trick pony, but the standard OU assault vest set is a great answer to Charizard Y, Mega Gengar, Koko, Lele, and Volcarona (that's over half the A+ tier btw) as well as Greninja, Primarina, Fini, and Thundurus-T.
He can even pick off...