I've been working on this duo for a while and it is finally ready. Here is my contribution:
Regigigas@Lum Berry
Nature: Adamant
Ability: Slow Start
EV Spread: 6 Attack . 252 Defense . 252 Special Defense
-Psych Up
-Rock Slide
-Crush Grip
-Drain Punch
Why are all the EVs in the Defense department? They are there to simply keep Regi alive and provide optimal recovery with Drain Punch. It has an attack stat of nearly 400 and a speed of 236 (without Slow Start) - I will explain the moveset later. It is usually my 3rd Pokemon in play, which is paired with:
Drifblim@Leftovers
Nature: Bold
Ability: Unburden
EV Spread: 252 HP . 129 Defense . 129 Special Defense
-Stockpile
-Skill Swap
-Swagger
-Baton Pass/Shadow Ball/Rest
I start with Drifblim and Togekiss/Clefable. Drifblim Stockpiles away while the other uses Follow Me and then Protect to hopefully fool opponents who aim for Togekiss/Clefable again. The balloon can usually get in 2+ Stockpiles before its fate-ridden partner takes the plunge. Now, insert Regi here.
Strategy: After a few Stockpiles, Drifblim is more than capable of taking a few hits (as is Regigigas). It immediately Skill Swaps while Regigigas copies its defensive boosts with Psych Up (one of its few stat-boosting moves). Then, Drifblim uses Swagger, (which is on several of my pokemon in case it fails) to activate the magic:
Regigigas receives a 2X boost to Attack and recovers from confusion with its Lum Berry. At the same time, it receives a 2X boost to Speed with its new Unburden ability. From here on, Regigigas destroys any wall with Crush Grip and can recover a great deal of HP on Tyranitars and Weaviles with Drain Punch. Finally, Rock Slide is simply amazing. With a speed stat of 472 and an attack stat of almost 780, not much lives - and if it does, it usually flinches.
From here on, Drifblim can Baton Pass to another Sweeper (if it lives), or Rest up for another partner to use Psych Up if Regigigas dies.
It takes a lot of skill and prediction to set this combo off and it took a lot of time to get here, but the results are beyond extreme. You simply have to see it in action to understand its full potential.