(Since I don't know which generation this is for, in some cases I'll put more than four moves, so you can choose the replacement)
Umbreon
Role: Tank
IVs focusing in HP, EVs in HP and defense
Ability: Syncronize
Item: Leftlovers
Moves:
Toxic
Moonlight
Double Team/Swagger/Confuse Ray/Curse
Payback/Feint Attack
Sylveon
Role: Setup/Support
IVs focusing in HP, EVs in HP and defense
Ability: Cute Charm
Item: Lum Berry/Babiri Berry/Kebia Berry
Moves:
Light Screen
Reflect
Helping Hand
Moonblast
Damage set 1:
Flareon standard set
Role: Damage (to defeat one at a time)
IVs focusing in attack, EVs in attack and speed or attack and HP (It can use both HP or speed to take the upper hand, I recomend speed, but the two things will work)
Ability: Guts
Item: Toxic Orb, Focus sash, Life Orb (Life Orb or Focus Sash, only if you can't have the one with that ability)
Moves:
Flare Blitz
Dig
Facade/Last Resort (Facade if its ability is Guts, Last Resort if is Flash Fire.)
Superpower/Iron Tail/Work Up/Quick Attack
Flareon set for ORAS only
Role: Damage (for hit more than one target at the same time)
IVs focusing in special attack, EVa in special attack and speed or special attack and HP
Ability: Flash Fire
Item: Life Orb/Focus Sash
Moves:
Heat Wave
Shadow Ball
Hyper Beam/Sunny Day (Don't worry about Sunny Day giving trouble to Vaporeon, since Flareon has a fire move, he can cover her weakness of grass)
Double Team
Vaporeon
Role: Damage
IVs focusing in HP, EVs in HP and special attack
Ability: Water Absorb
Item: Wide Lens/Waterium Z
Moves:
Hydro Pump/Scald
Blizzard
Shadow Ball
Hyper Beam
--
Now, a combination of Vaporeon and Jolteon as an alternative to use with Umbreon and Sylveon, instead of Flareon
Damage Set 2:
Vaporeon
Role: Damage
IVs focusing in HP, EVs in HP and special attack
Ability: Hydration
Item: Wide Lens/Waterium Z
Moves:
Hydro Pump/Scald
Blizzard
Shadow Ball
Hyper Beam
Jolteon
Role: Damage/Damage support
IVs focusing in speed, EVs in speed and special attack
Ability: Volt Absorb or Quick Feet
Item: Focus Sash
Moves:
Rain Dance
Thunder
Shadow Ball
Hyper Beam/Signal Beam
Quick notes: I'm using Hyper Beam a lot with this team because, sometimes, you need to defeat your enemy before he defeats you in one hit, and, if he endures your first hit and defeats you with one hit, you'll never have the chance to hit him twice to finish the job. Having Giga Impact or Hyper Beam could give you the support you need when you don't have a wide movepool. I learned that the hard way! And work very well for me
