>>14907553A lot of pokemon in NU are viable in OU.
I've used Miltank and Jumpluff to some degree of success (specially Miltank, who's an absolute beast). Swasbuck and Victreebel in the sun, Parasect in the rain, Ludicolo as a rain counter, Jynx, Golurk... these are all viable if you play to their strenghts, though they're sometimes hard to use and if you expect them to do more than what they're supposed to they could end up disappointing.
Liepard can sweep whole teams with some luck and I've done it several times, but I guess it doesn't count as it's a completely luck based strategy. Murkrow can do the same, too.
As for RU pokemon, a lot more are usable in OU. Starting from Amoonguss, who's standard in sand defense, and Sandslash who's standard in sand offense. Kabutops is a great offensive spinner and puts a number to rain teams. Aerodactyl, Omastar, Crustle, hell you may even tell me it's shit but I've seen Flame Charge Magmortar in action and it can decimate teams on it's own.