The opponent sent out Haxorus!
Umbreon used Curse!
BEST CASE:
The foe's Haxorus used Dragon Dance! (predicting your hard switch)
Umbreon used Baton Pass! Go, (insert somewhat bulky physical attacker here!)
Haxorus used Outrage! Bulky physical attacker took damage but survived thanks to the Curse boost.
BPA used STAB move! Haxorus fainted!
MEDIUM CASE:
Umbreon, return! Go, Choice'd Pokémon!
Haxorus used Taunt! CP fell for the Taunt!
CP used STAB move! Haxorus fainted!
Or WORST CASE:
Haxorus used Taunt!
Umbreon can't use Baton Pass after the Taunt.
Umbreon, return! Go, Focus Sash/Choice Scarf Pokémon!
Haxorus used Dragon Dance!
Haxorus used Outrage (if Focus Sash'd)!
Focus Sash'd Pokémon held on with its Focus Sash!
FSP used STAB move! Haxorus fainted!
(else, CS'd Pokémon outspeeds and OHKOes)
So the WORST CASE scenario is that your Sash'r is brought down to one or you have to lock your Scarfer prematurely. "But what if your Scarfer/FS'r is dead?" Team Preview exists, folks. If you see a Haxorus, SAVE THEM FOR IT. "What if I don't have one?" A team withut a revengekiller is not well put together, sorry mate.
Umbreon is not that good - I know that, the OP knows that, all y'all obviously know that. But just saying "He's worthless without Foul Play, don't use him" is pretty close-minded and negative of y'all and it doesn't help the OP with his problem. We should endeavor to help him find ways to use his favorite Pokémon, not discourage him by saying it's worthless. A bad Pokémon still has its uses and can fill a niche - like I mentioned earlier, Umbreon walls Bisharp, who is one of the best Pokémon in the game right now. Maybe the OP could build a team using threatening sweepers that might not work well together because they are Bisharp-weak, then use Umbreon to offset that and allow them to be used on the same team. Not to dish on you guys, but we should encourage experimentation with all sorts of Pokémon, even the 'bad' ones.