Also for skarmory, i use 252 hp/ 252 defense impish as a physical wall with the standard:
Leftovers
Drill peck/ brave bird
Spikes
Whirlwind
Roost
Im sure there is a more viable set but this one is pretty basic that works well against: Non Mix-rayquaza, NOn fire punch groudon, Garchomp, bulk up dialga, most giratina (if you don't mind being burned). All these you can set up spikes easily.
Ok, I'll post my Skarmory sets. I have two sets; a physically defensive, and a specially defensive one.
Nature: Impish
Item: Leftovers
Spikes
Roost
Whirlwind
Stealth Rock / Toxic
EVs - 252 HP / 216 Def / 40 SDef
OR
EVs - 252 HP / 16 Def / 240 SDef
A description of this set is in the Uber Discussion thread. I'll mention some things that I didn't discuss before. Toxic is an option over Stealth Rock, for there are many pokemon that can set up Stealth Rock. Toxic can be used to hit incoming Kyogre and other pokemon that will definitely force Skarmory out.
The first set of EVs is easier to use, and is best suited for physical attackers, mainly Groudon, Rayquaza and Garchomp. The second set utilises Skarmory's fantastic Steel typing on the special sides of things, making him a great switch-in to locked Dragon attacks, and in emergencies, Latias that lack Thunder. I prefer the first set, but I'm still posting the second EV spread, because Jibaku stated he has used it well. And it still easily walls Groudon and Garchomp. Rayquaza is slightly harder.
Here's some damage calculations, just to get a feel of the sets:
Impish 252 HP / 216 Def / 40 SDef
+1 LO Adamant Rayquaza's Outrage: 40.42% 43.71% 47.60%. With SR down and one turn of Leftovers recovery, that's a 2.04% chance of a 2HKO
+2 LO Adamant Rayquaza's Dragon Claw: 35.93% 38.62% 42.22%
+2 LO Adamant Rayquaza's Waterfall: 47.90% 51.80% 56.59%. With one turn of Leftovers recovery and no SR, that's a 30.51% chance of a 2HKO.
LO Adamant Groudon's Stone Edge: 30.24% 32.63% 35.63%
LO Adamant Groudon's Fire Punch: 67.07% 72.46% 79.04%
Timid Palkia's Spacial Rend: 27.84% 30.24% 32.93%
Specs Timid Palkia's Spacial Rend: 41.62% 44.91% 49.10%. With SR down and one turn of Leftovers recovery, that's a 14.66% chance of a 2HKO.
108 SpA (standard) Timid Latias' Dragon Pulse: 32.93% 35.93% 38.92%
Timid Palkia's Surf in the rain: 83.53% 90.12% 98.20%
Impish 252 HP / 16 Def / 244 SDef
+1 LO Adamant Rayquaza's Outrage: 46.71% 50.90% 55.39%. With SR down and one turn of Leftovers recovery, that's a 99.41% chance of a 2HKO
+2 LO Adamant Rayquaza's Dragon Claw: 41.62% 44.91% 49.10%. With SR down and one turn of Leftovers Recovery, that's a 14.66% chance of a 2HKO.
LO Adamant Groudon's Stone Edge: 34.73% 37.72% 41.02%
LO Adamant Groudon's Fire Punch: 77.84% 84.43% 92.22%
Timid Palkia's Spacial Rend: 19.76% 21.56% 23.35%
Specs Timid Palkia's Spacial Rend: 32.93% 35.63% 38.62%
Timid Palkia's Surf (no rain): 39.82% 43.11% 47.01%
108 SpA (standard) Timid Latias' Dragon Pulse: 23.35% 25.45% 27.84%
Scarf Lead Mewtwo's Focus Blast: 44.31% 48.20% 52.40%. This will never 2HKO without SR thanks to Leftovers. (With SR and one turn of Leftovers, it's 77.19%, but remember that this Mewtwo is used as a lead)
LO 0 SpA Hasty Rayquaza's Flamethrower: 75.45% 82.04% 89.22% (In other words, avoid Fire attacks, even in the rain)
Standard Latias' Thunder: 91.62% 98.80% 107.78% (Never try to take a Thunder)
Now, I'll start testing Mamoswine. I made this up using theorymon, and it has NOT been tested yet. I will test it over the next few days; I'm just posting it in case anyone wants to try it for themselves:
Ability: Snow Cloak
Nature: Impish
Item: Leftovers
Earthquake
Ice Shard
Avalance
Filler - Superpower, Toxic or Stealth Rock could do
4 HP / 252 Atk / 252 Def
This Mamoswine is very physicall defensive, but only a Bold Mamoswine can switch into a LO Adamant Rayquaza Outrage and always survive, even with SR in play. In turn, Mamoswine's Ice Shard deals 90.03% - 107.12% to 0 HP / Def neutral nature Rayquaza, which means Rayquaza will always be OHKOed after one turn of LO recoil.