Sylveon's cute and cuddly appearance belies an impressive ability to stand up to the monstrous special threats roaming the Ubers metagame. Packing an impressive base 130 Special Defense backed by base 95 HP, as well as access to coveted support moves such as Wish and Heal Bell, Sylveon works excellently as a wall and team supporter, holding back threats such as Palkia and Yveltal while providing invaluable cleric support. A Pixilate-boosted Hyper Voice gives Sylveon a decent punch for a defensive Pokemon, ensuring it doesn't become setup bait for the threats that it is meant to check. That being said, Sylveon suffers from a mediocre Defense stat, and it cannot do much against trappers such as Mega Gengar and Wobbuffet, leaving it rather vulnerable. It also faces heavy competition from Xerneas, which has equal or better stats in all categories and can also provide cleric support via Aromatherapy. However, Wish gives Sylveon an important edge that makes it much more of a team player than Xerneas. If you are in need of a bulky Fairy-type that can check prominent special attackers and provide invaluable cleric support, Sylveon certainly won't disappoint.
move 1: Wish
move 2: Protect
move 3: Heal Bell
move 4: Hyper Voice
evs: 252 HP / 4 Def / 252 SpD
Thanks to its solid HP stat, Wish allows Sylveon to patch up its teammates that either need healing or are coming in to absorb an attack aimed at Sylveon. Combined with Protect, Wish also provides Sylveon with reliable recovery for itself. Protect also allows Sylveon to garner more Leftovers recovery and scout possible Choice attackers. Heal Bell cures Sylveon and its teammates of debilitating status conditions. Hyper Voice becomes a 117 Base Power STAB attack thanks to Pixilate, OHKOing Darkrai with ease while also doing about 70% to Palkia, Yveltal, and Mega Mewtwo X. Hyper Voice also pierces Substitute, making it useful against common users of the move such as Darkrai and Shaymin-S.
Always maximize HP and Special Defense, as Sylveon needs the investment to properly handle threats. To give an example of how specially bulky Sylveon is, Life Orb Yveltal cannot 2HKO Sylveon with any move. Sylveon is also a fine check to Palkia, as Lustrous Orb sets cannot 2HKO it, assuming it is not raining. However, if it is raining, an unboosted Hydro Pump or a Lustrous Orb-boosted Surf can potentially 2HKO Sylveon, so be careful. However, Sylveon is not 2HKOed by Modest Choice Scarf Kyogre's Surf in the rain, allowing it to stall out the rain turns with Wish and Protect. Leftovers is the preferred item as the passive recovery goes well with Wish and Protect.
Sylveon should be used on balanced or stall teams that need a solid special wall and clerical support through Wish and Heal Bell. It makes a solid switch-in to threats such as Yveltal, Palkia, both Giratina formes, Darkrai, Kyurem-W, and Dialga lacking Flash Cannon, and it can also come in on defensive Pokemon such as support Arceus or Lugia and use Heal Bell or Wish. Sylveon can also check certain Fighting-types in an emergency—it can take one Stone Edge from Choice Scarf Terrakion and barely survives +1 Mega Mewtwo X Psycho Cut at full health—but under no circumstances should it be relied upon to check these threats, as it has very mediocre Defense.
Tread lightly with Sylveon around teams with Mega Gengar. If Sylveon is caught in a bad situation or on the wrong end of a double switch, Mega Gengar can trap Sylveon with Shadow Tag and either cripple it with Taunt or snipe it with Sludge Bomb. If you don't have a Pursuit user on your team to get rid of Gengar as it Mega Evolves, be very careful with Sylveon once Gengar has Mega Evolved.
Mega Gengar is Sylveon's worst enemy, as it traps it easily and KOes it with Sludge Bomb, so packing a Pursuit user on your team to make Gengar less of a problem is highly advised. Mega Scizor is generally the best answer as it can come in easily on Taunt or Sludge Bomb and checkmate Gengar with Pursuit and/or Bullet Punch. As a bonus, Mega Scizor highly benefits from Sylveon's clerical support and can check dangerous sweepers that can set up on Sylveon, such as Geomancy Xerneas and Swords Dance Arceus. Mega Tyranitar can also Pursuit trap Gengar, although it is less reliable as Focus Blast will destroy it. Mega Tyranitar does have the advantage of checking Ho-Oh, which can easily come in on Sylveon. Rock and Water Arceus can also check Ho-Oh well and can burn physical attackers that might try to take advantage of Sylveon's low Defense. Support Arceus formes generally benefit greatly from Heal Bell to remove Toxic. Thanks to Multiscale, Lugia can take on all versions of Swords Dance Arceus, Geomancy Xerneas, and Ho-Oh, and it appreciates Sylveon's Heal Bell and ability to take on Dark-types.
Sylveon can't touch Steel-types at all, so switch-ins to them are also highly recommended. Groudon and Landorus-T work excellently as both have no recovery of their own and thus highly appreciate Wish, as well as Heal Bell to cure them of possible burns. Do note that it is not recommended to use Gliscor, as Heal Bell hurts it by denying it a turn of Poison Heal recovery upon switching back into battle. Fire-types such as Ho-Oh and Heatran can also work well.
Any Pokemon that relies on Rest for recovery loves Heal Bell support to cure them of sleep. As such, Kyogre and Giratina are solid partners:. Kyogre can take on most bulky Steel-types, and Giratina appreciates Sylveon's immunity to Dragon-type attacks and can take on Swords Dance Arceus, and both of them can handle Ho-Oh to an extent.
Shed Shell foils Mega Gengar, Sylveon's primary nemesis, by negating Shadow Tag, but losing the passive recovery of Leftovers reduces Sylveon's walling capabilities. If you are willing to forgo Heal Bell, Baton Pass is a nice momentum-preserving tool that makes Wish passing easier and can let Sylveon escape from predicted Mega Gengar switch-ins. Toxic enables Sylveon to outstall bulky tanks and cripple Ho-Oh on the switch, but it is generally not recommended as it doesn't do anything to the Steel- and Poison-types that comprise Sylveon's main checks. Yawn works as a sort of phazing move and can be used to potentially put a check to sleep, but as a pure phazer, Xerneas is generally better. Shadow Ball 2HKOes Gengar on the switch and gets decent chip damage against Aegislash, Jirachi, and Bronzong, but it has little use otherwise. Calm Mind is a decent option when combined with Baton Pass to give monsters such as Kyogre or Palkia a nice boost.
Finally, Sylveon does have large enough movepool to make use of Choice Specs, but Xerneas and Fairy Arceus highly outclass Sylveon at offensive roles, so these should never be seriously considered.
Checks & Counters
**Mega Gengar**: By far Sylveon's best counter, as Shadow Tag prevents fleeing, Taunt shuts down recovery attempts, and Sludge Bomb 2HKOes with ease. Gengar also resists Hyper Voice so it can switch in fairly easily, Mega Evolve, and KO Sylveon.
**Steel and Poison Arceus**: Both formes resist Hyper Voice, are immune to Toxic, and pack a super effective STAB Judgment. Should they have Calm Mind, they can set up against Sylveon.
**Bulky Steel-types**: Sylveon can't touch Steel-types, so most of them can switch in freely and set up on it, or just wreck it with their STAB attacks. Scizor, Aegislash, Bronzong, Jirachi, Heatran, Ferrothorn, and Excadrill all work nicely. Skarmory works too if it has Taunt.
**Ho-Oh**: Ho-Oh can switch in on Sylveon easily and destroy it with Sacred Fire.
**Bulky Setup Sweepers**: Setup sweepers that don't fear Hyper Voice can use Sylveon as setup bait. Geomancy Xerneas and Swords Dance Arceus are the most notable examples.
**Powerful Physical Attackers**: Powerful physical attacks do a lot of damage to Sylveon due to its mediocre Defense. Groudon and Landorus-T are good users of these as they have enough bulk to take a Hyper Voice or two on the switch.
**Roar and Whirlwind**: These moves are annoying for Sylveon as they pierce Protect, which can prevent it from healing itself with Wish. Lugia, defensive Kyogre, and Groudon are notable examples of Pokemon that often carry these moves.