Sylveon

Sylveon is one of the best wallbreakers in the UnderUsed tier thanks to Pixilate Hyper Voice being able to blast past frail resistant Pokemon. Its mono-Fairy typing allows it to switch into strong and powerful Dark-, Dragon-, and Fighting-type moves such as Hydreigon's Draco Meteor and Heracross's Close Combat. Sylveon's 95 / 130 special bulk allows it to check some moderately powerful special attackers even if uninvested. Sylveon also gives Florges competition as a cleric, since it has more physical bulk and a more powerful STAB attack. It does, however, lack one-turn recovery unlike Florges. Unfortunately, Sylveon's physical bulk is decidedly mediocre when uninvested, meaning that most strong neutral attacks, and even some resisted ones, can 2HKO it. Also, most Dragon-types generally carry coverage for Fairy-types, meaning Sylveon has to play carefully around them. Furthermore, Sylveon is also held back by a less than stellar base 60 Speed, meaning it can't do much against faster teams that apply a ton of offensive pressure.