Moves
Foul Play is Umbreon's most reliable STAB move; it allows Umbreon to significantly damage physical attackers such as Scizor, Mamoswine, and Mega Beedrill. Heal Bell heals Umbreon's teammates and itself from status ailments, which also makes Umbreon a more reliable special wall. Toxic not only gives Umbreon an easier time beating setup sweepers, such as Latias, but also lets it badly poison common switch-ins, such as Terrakion and Infernape, and slowly wear them down. Wish allows Umbreon to recover its own health as well as heal its teammates up. Protect combines with Wish to give Umbreon an easier time healing itself up and also allows Umbreon to scout common Choice item users, such as Hydreigon and Infernape, and gain more recovery from Leftovers. Alternatively, Moonlight gives Umbreon a more reliable form of self-recovery; in combination with Wish, Umbreon can use Moonlight on a turn it would otherwise use Protect on and gain more health back. However, Moonlight's low PP means Umbreon can be stalled out rather easily.
Set Details
Maximum investment in HP and Special Defense, combined with a Calm nature, allows Umbreon to take on special attackers such as Latias, Hydreigon, and Nidoqueen as easily as possible. 4 Speed EVs allow Umbreon to outpace uninvested Scizor and hit it with a Foul Play before it gets to hit Umbreon with a super effective move. Synchronize allows Umbreon to punish certain Toxic users such as Rotom-H, Slowbro, and Swampert that attempt to badly poison it. Leftovers provides passive recovery, which helps Umbreon retain longevity.
Usage Tips
Switch in Umbreon on special attackers such as Latias, Hydreigon, and Nidoqueen and beat them via attacking with Foul Play when ever Umbreon is at a comfortable amount of HP; this is achieved by continuously using Wish in tandem with Protect or Moonlight. Hence, Umbreon needs to stay as healthy as possible throughout the match. Generally, you should use Wish either when Umbreon is low on HP or when a teammate should be healed up. Use Protect to scout for potential mixed special attackers with Fighting coverage, such as Superpower Hydreigon and Nidoking, and Choice-locked Pokemon like Latias and Volcanion. Be wary of using Protect against certain potentially Choice-locked Pokemon that may utilize setup moves, such as Scizor and Terrakion. In addition, be wary of switching in Umbreon on potential Trick users such as Togekiss and Latias. Umbreon could also be switched in on certain physical attackers, such as Mega Aerodactyl and Mega Sharpedo. Avoid spamming Foul Play against teams with Justified users such as Cobalion, Terrakion, and Lucario, as they can easily take advantage of it to boost their Attack. Despite its access to Toxic and Foul Play, Umbreon heavily struggles to beat certain setup sweepers such as Cobalion and Terrakion that beat it by virtue of their typings. Hence, it is wise to not stay in on them, as they use Umbreon as setup fodder. Do not stay in on Taunt users, such as Krookodile and Jellicent, because they can reliably shut down and beat Umbreon. Use Heal Bell when either Umbreon or its teammates are afflicted with a status ailment, such as Toxic, while keeping in mind Heal Bell's low PP.
Team Options
Umbreon fits well on balance and stall. Fairy-types, such as Mega Altaria and Togekiss, and Flying-types like Moltres and Crobat can handle Fighting-types such as Infernape and Cobalion. The aforementioned Fairy-types can also utilize Heal Bell so Umbreon can freely run Toxic, and the Flying-types appreciate Umbreon's Wish support because of their Stealth Rock weakness. Entry hazard removers such as Gligar and Tentacruel ensure that Umbreon won't have to take residual damage each time upon switching in. The latter pairs exceptionally well with Umbreon not only because it can take on certain physical attackers that scare Umbreon out, such as Cobalion and Scizor, but also because it removes Toxic Spikes by virtue of its Poison typing. Physically defensive Pokemon like Swampert and Mega Slowbro pair well with Umbreon thanks to their ability to handle the majority of physical attackers, such as Infernape and Cobalion. They are also capable of punishing common Taunt users like Krookodile with a potential Scald burn. Additionally, wallbreakers, such as Scizor, Volcanion, and Primarina, appreciate Umbreon's Wish support and also scare out setup sweepers that attempt to set up on Umbreon.