I'd just like to say that Regigigas is almost broken in the NU metagame. It can really save you from losing the game, as all it needs to do is spread some paralysis, confuse its opponents, set up some Substitutes, and sweep. Sure it lacks recovery and has a horrible ability, but that doesn't mean it can't be useful. I use Regigigas on one of my best NU teams, and it constantly does a fantastic job at sweeping. The best set you can possible use, in my opinion, with Regigigas would be this:
Regigigas @ Leftovers
Ability: Slow Start
EVs: 252 HP/76 Def/180 SDef
Impish nature (+Def, -SAtk)
- Thunder Wave
- Confuse Ray
- Substitute
- Return
I'm sure all of you will scream at me and say that this set is completely bait to Ghost-types. Yes, that's true. Substitute Haunter kills this set easily; however, it can't necessarily switch in safely, as it can be caught with Thunder Wave (or Confuse Ray then Thunder Wave if it hits itself). I'd say that Dusclops is the only surefire counter to this set. It can Rest off status ailments, is immune to Return, and can use Seismic Toss to bring down Regigigas. This is one of the reasons why I use Skuntank in conjunction with Regigigas because it can take out Ghost-types. Also, I use Vileplume to absorb Toxic Spikes, even though they aren't as common due to the departure of Cloyster.
The EV spread is what makes Regigigas such a top-notch threat to any team. With its amazing base 110 HP, 110 Def, and 110 SpD stats, Regigigas is ridiculously hard to OHKO. With this EV spread, Regigigas hits 424 HP, 302 Def, and 301 SpD, which is pretty awesome. This allows it to survive even Primeape's Close Combat and return with an OHKO with Return. This also lets Regigigas set up against weak attackers, such as Slowking, as they can't break Regigigas's Substitute. Even without any Attack investment, Regigigas's base 160 Attack stat is high enough to make it deal enough damage to sweep effectively (it can still score many OHKOes and 2HKOes once out of Slow Start).
Regigigas's hindering ability is accommodated by the parafusion combo, which works like a charm. I just can't stress it enough how insane Regigigas is. Once this beast sets up, good luck taking it down.