Here's that Regigigas set I was using in the early stages of the new UU:
Regigigas @ Leftovers
Ability: Slow Start
Nature: Adamant
THUNDER WAVE
SUBSTITUTE
RETURN
EARTHQUAKE
EVs: 252 HP, 252 Atk, 4 Def
The idea is to either a) bring this in on a choiced ghost attack or b) come in when your entire team has been wiped out for a last-ditch charge. Then use Thunder Wave on whatever comes out to meet you, or take the time to throw up a sub. If they switch, TW them again. If they attack, throw up another sub. Reggies subs are not broken by Seismic Toss, so ST Regice can be set up on with 'ease'. Rinse and Repeat until Reggie gets its act together. With luck your opponent will have switched its fast things into a Thunder Wave, so Giggy can cruise through the opponent's team, provided of course it is faster than everything else. Normal + Ground is a powerful combination in UU, a tier devoid of Skarmory, Bronzong and Gengar. The only real worries this set has are Mismagius and Physical Walls.
MISMAGIUS: If you have a sub up, Thunder Wave and run. If not... run. If you're in a last stand position... annoy the opponent by repeatedly subbin'
PHYS. WALLS: Monstrous as he is, Regirock lacks the raw power to smash everything in his path. Without Life Orb, boosting moves and other sweeper needs, he's not ploughing through mid-game. Eliminate walls before proceeding.
Well, that's the theory. In practice, he was remarkably easy to get into play AND to rid himself of Slow Start, but he's not the sort of sweeper that can charge headfirst into battle again and again. Once the surprise is gone, and you switch out, he has barely enough health to repeat. He was easily walled by Weezing and Regirock and had too little type coverage.
Conclusion: If someone can make a working team with Giggy... They're welcome to it.