with umbreon, it really doesn't need a specific nature. i'd personally go with a +Defense nature, those of which do not lower Sp. Def. but hey, if you want an Umbreon to do some damage while it wishpasses and takes in special hits, then i suggest the following moveset:
Umbreon @ Leftovers/Lum Berry
Careful/Sassy Nature
252 HP/212 SP DEF/44 DEF
-Faint Attack
-Curse
-Mean Look
-Wish
the plan: trap a special sweeper like Starmie or a special wall like Blissey who doesn't usually have a supereffective hit against you with Mean Look. then max out your Attack and Defense with Curse. use Wish every one or two Curses to stay alive just in case they hit you with a supereffective hit, or in case of Blissey, has Seismic Toss. once you maxed out your attack and defense with 6 Curses, start firing away with Faint Attack. though it's not a very strong move, it will never miss and it hits EVERY type. aside from that, it gets STAB.
this strategy comes for a surprise sweep at the end of the battle right before you enter a stall war. i hate stall wars myself, so i like strategies like this. be careful not to leave umbreon in with sweepers who have SE hit against it or who have Swords Dance/Nasty Plot.
