I still say you are sort of snubbing Onix for play in NU. :/
Well... I'm not saying that I'm snubbing Onix from NU. Heck, defenses are impressive (with Stone + Sandstorm 272 HP, 534 Def, 465 SpD with Max HP/Max SpD Positive), however the problem here is... this pathetic base attack. Even after 2-3 curses it can't threaten fly. 45 base Attack just doesn't cut it. If it has at least 60-70 base Atk, then history would be different.
i think the best candidate for this are misdreveus (yeah GSC Trapper ftw)
Well, I see one more interesting set for Misdreavus in future NU/UU.
'Bulky Nasty Plotter'
Misdreavus @ Pre-Evolution Stone
Nature: Timid Nature
EVs: 252 HP / 36 / 216 Speed
~ Pain Split
~ Nasty Plot
~ Shadow Ball
~ Thunderbolt
Obviously this set hates status, so avoid it at any cost. Pain Split is perfect move, as you need recover for this. 216 Speed is enough to outspeed positive 80's. This guy reaches 324 HP/234/309 defenses which is pretty solid. On special side this guy has similar bulk to Max HP Milotic, which is nice and on physical misses a bit against Defensive Blastoise. Strategy is simple - just try to Nasty Plot to +6 and sweep. It's quite funny thing that standard 84 Atk EVs Pursuit on Scarf Houndoom deals... 27.78% -> 33.33% when you don't switch out, so you may even set-up on it. Anyway, on paper looks solid.