>>17888577+1 4 Atk Genesect U-turn vs. 252 HP / 0 Def Umbreon: 246-290 (62.4 - 73.6%) -- guaranteed 2HKO after Leftovers recovery
It's Scarfed and it gets the Download boost. Unless it switched directly in, Genesect is going to inflict pain.
4 Atk Umbreon Foul Play vs. 252 HP / 0 Def Conkeldurr: 93-111 (22.4 - 26.8%) -- 30.6% chance to 4HKO
That's what happens when you try to attack Conkeldurr directly.
252+ Atk Conkeldurr Drain Punch vs. 252 HP / 0 Def Umbreon: 264-312 (67 - 79.1%) -- guaranteed 2HKO after Leftovers recovery
And that's regaining more HP than it loses to Foul Play each turn. If, instead of mashing Foul Play, you selected Toxic...
252+ Atk Guts Conkeldurr Drain Punch vs. 252 HP / 0 Def Umbreon: 392-464 (99.4 - 117.7%) -- 93.8% chance to OHKO
...you get your shit pushed in the instant you hit anything other than Protect.
252 Atk Adaptability Mega Lucario Close Combat vs. 252 HP / 0 Def Umbreon: 524-620 (132.9 - 157.3%) -- guaranteed OHKO
This one takes less than 40% from Foul Play. It can switch in with impunity.
+2 252 SpA Adaptability Mega Lucario Aura Sphere vs. 252 HP / 252+ SpD Umbreon: 444-524 (112.6 - 132.9%) -- guaranteed OHKO
This one takes less than 30% from Foul Play. It switches in, sets up, and then kills the rest of your team.
Half of that team takes your "invincible" Umbreon and flat-out kills it. Hell, Talonflame deals ~40% as it U-Turns to Conkeldurr. Skarmory vomits hazards all over you, Roosts a bit, and then pushes you aside with Whirlwind. The only thing that you actually beat would be Rotom-W, and that's only if it doesn't have Rest (which it would run for the express purpose of laughing at you after a successful WoW, in addition to actually being pretty good in the absence of Pain Split).
4 Atk burned Umbreon Foul Play vs. 252 HP / 0 Def Rotom-W: 30-36 (9.8 - 11.8%) -- possibly the worst move ever
How in the world did you manage to kill that team with that Umbreon? I'm astounded.