Sylveon

Sylveon is a decent pick on Fairy teams thanks to its amazing wallbreaking capabilities with its Pixilate ability, good base 110 Special Attack, and Choice Specs. Furthermore, good special bulk allows it to fire off Choice Specs-boosted Hyper Voices with ease against special attackers, and good coverage options such as Psyshock allow Sylveon to deal massive damage to types that would usually annoy Fairy, such as Poison. However, Sylveon's low Defense and Speed stats make it vulnerable to physical attackers and revenge killers and unable to outspeed key threats. Sylveon's mono-Fairy typing compounds this by adding nothing defensively to Fairy teams, and Sylveon cannot switch into common threats to Fairy. Sylveon is also very vulnerable to residual damage and is worn down very fast, making it susceptible to revenge killers. Lastly, while it has good coverage options, Sylveon lacks a way to heavily damage most Steel-types outside of Hidden Power, which is a crippling trait for a Fairy-type. All of these traits make Sylveon generally hard to fit on a team.