Unheard of except for, y'know... Slaking.
Regigigas' issue is that he relies on luck too much to set up; He doesn't get Rest (or any recovery for that matter), and needs to use parafusion to stall out the turns until Slow Start ends. There's no reason to roll the dice with him when Slaking can hit that hard right off the bat. Add in the fact that T-Wave + Confuse Ray only leaves you with two moveslots, he's not viable, even with his massive base stats.
Jynx, on the other hand, could tear things up. A good dual STAB, a Sleep-inducing move, and 115 base SpA paired with 95 Base Spe? Yes please. Her only problem is that she's forced to pick between HP Ground for Steels and HP Grass for Slowking, but this problem is somewhat lessened because she can put one counter to sleep. A set like this could be viable:
Jynx@Life Orb
Ability: Dry Skin
Timid Nature, 252SpA/4SpD/252Spe
Psyshock
Ice Beam/Blizzard
Lovely Kiss
HP Ground/HP Grass
This set is an all-out attacker, and can hit both defenses because of Psyshock. Ice Beam is the preferred Ice STAB, but Blizzard can be used when paired with Hail. Lovely Kiss puts a counter to sleep, while you Hidden Power can take care of something that can otherwise counter you. Life Orb is the best item since Jynx's defenses are laughable at best. Even with those defenses, Dry Skin can give her a free switch-in on Water moves; the drawback is minor since Fire moves will kill her anyways. Nasty Plot could potentially find its way on here too.