Well, I wanted to somehow add this into the main site or at least make it a little more well know, but i'm a little skittish abouting posting in the Analysis Workship so i'm just going to go post it here.
** Supporting Groudon **
Groudon @ Leftovers
Ability: Drought
EVs: 252 HP / 32 Defense / 60 SpDef / 8 Spe / 156 Atk
Adamant nature (+Atk, -SAtk)
- Earthquake
- Dragon Claw / Fire Punch
- Toxic
- Stealth Rock
Toxic, or being badly poisoned is one of the worst status effects in the game, to inflict a wall with. The only ones that are immune from Toxic, Poison or Steel types, however will be slammed hard by super effective Earthquake and Fire Punches.
The premise of this set is to lure in walls like Lugia, Latias, Deoxys-D and break them with Toxic. All three of these top-tier Uber Walls rely on instant-recovery moves like Roost or Recover making them very susceptible to status effects like Toxic. And the walls that are immune to Toxic, Dialga, Forretress and the ever rare Skarmory all take a hefty beating out of Fire Punch or Earthquake. The only real, Wallish counter to this set is Giratina who can simply rest of damage and your Toxic whilst threatening you with a Will-o-Wisp. Stealth Rock is mostly there for scouting, but you'll also be hard pressed to find a Stealth Rocker as capable as Groudon, whilst again putting the pain on the almost omnipresent Lugia.
Whilst this set won't be sweeping, personally any time soon it can certainly open up doors for other Physical powerhouses like Rayquaza or Bulk Up Dialga to rampage through a team.
Now for a little explanation on the EV spread. The Defensive EVs are very, specifically optimised. 252 HP allows for maximum durability in this set, allowing Groudon to take hits better from both sides. The EV in defence allow Groudon to survive a DD'd Life Orb Rayquaza's Outrage (59%-70%) making it a decent counter.
Many will be thinking, SpDef EVs on Groudon? But those numbers were intended for two very common, switch-ins Lugia and Latias. The small investment of SpDef ensures that Lugia's ice beam is a mere 4HKO giving you ample time to set up Stealth Rocks on the switch in and Toxic as it either puts a Reflect or tries to nail with an Ice Beam.
These will also let your Groudon become 3HKO'd by Latias' Dragon Pulse (33%-39%) after factoring Soul Dew and Leftovers. In the mean time, you will be able again, wear away at it's durability by Toxic'ing it or simply using Dragon Claw (60%-70%), dishing out a 2HKO. Also of note, you'll be able to just survive Latias' Grass Knot (83%-98%).
This set works remarkably well with WishBliss or WishLatias, lacking a reliable recovery move of it's own. The most common switch-in's to the aformentioned supporting special walls are strong physical sweepers like Groudon or Dialga, pokemon that SupportDon can wall fairly easily with high defence, at the same time Toxic'ing enemy Dons or just Earthquaking that Bulk Up Dialga as it attempts to set up in vain.
Remember, when using this set don't see it as either a wall or a sweeper. It should be treated as a Support pokemon similiar to Donphan or Swampert in OU. It's main job is to break through walls or bulky threats with Toxic, when that's complete you may switch to your "real" physical wall such as Lugia or Giratina and simply stall it out as the Toxic kills.
