Shiftry is actually a very powerful UU. Both of its nature is an awesome abililty.
Shiftry- [atk + / sp.atk -] @ lum berry (sunny day) / quick claw (non sunny day)
EV: (depends... very flexible depending on strategy)
-extrasensory
-3 of the following: sunny day, swords dance, explosion, brick break, quick attack, rest, aerial ace
Too much stuff to do... and the stats aren't all that bad.
Spinda... Err.... I do have a strategy in mind but the stats won't be agreeing with me...
Spinda- [def or sp.def + / atk-] @ leftovers
EV: distribute them in any defensive manner you want, in HP/def/sp.def
-teeter dance
-protect
-wish
-toxic
If extra attack power is needed to take care of natural cure users, use seismic toss somewhere (but have fun against recover o.o; )
Roselia with levle balance is quite strong actually... it's just a weaker version of Sceptile with spike and aromatherapy. Horrid defense and weird stats, with one of the best movepool ever
Roselia @ leftovers/quick claw (Natural Cure)
EV:
-leech seed
-protect/substitute
-ingrain
-spike
NOTE: super low defensive stats do not really support this at all... but however I'll imagine that it'll be fun to play. EV and nature are not supported because... you'll be needed some creativity to think of how this thing can ever survive a hit ^_^; You can also go with a sweeping Roselia with mixed abilities (its attack isn't all that bad, just the defense... ;_; )
Volbeat and Illumise both can't do much again due to stats... best to go with annoyer?... Tail Glow is awesome... but it'll take some major luck to survive 2 rounds of attacks after using tail glow (it's really not that fast even though that is the best stat it has)
Volbeat- [spd or sp.def+ / sp.atk -] @ lum berry/quick claw/leftovers
EV: Spd and Sp.def, some hp
-thunderwave
-light screen
-confuse ray
-seismic toss/silverwind/signal beam/quick attack
Illumise- [spd or sp.def+ / atk-] @ lum berry/quick claw/leftovers
-wish
-attract
-thunderwave
-thunderbolt/HP (special)
Hmm it just looks like a weaker version of Plusle/Minun to me, who are a weaker version of Raichu...
Mawile- [def + / sp.atk or atk-] @ leftovers/lum berry/quick claw (Intimidate)
EV: Hp and Def
-iron defense/swords dance
-baton pass
-fire blast/rock slide
-counter/toxic
*shrug* With defense boost and iron defense, it may work out to stall physical attacks not too bad (as long as there's no STAB quake/brick break... ahem). Fire blast for anti Skarm/something to do against Wheezing. Baton pass is always helpful.