You know how Bloo's Frontier team had specially defensive Gastrodon, Heatran, and Roserade, along with standard physically defensive Skarm, forming a near-impenetrable anti-weather wall? Want to meet a pokemon that threatens all four of them at the same time, and, with a good prediction or two, will take at least one out every time it switches in?
"Anti-Anti-Weather"
Empoleon @ Expert Belt / Wise Glasses
Torrent | Modest (+SAtk, -Atk)
12 HP / 252 SAtk / 104 SDef / 140 Spd
- Substitute
- Surf
- Grass Knot
- Ice Beam
First, the EVs. Max +nature SAtk is obvious to muscle through the walls' high defenses and score 1HKOs on the steels and 2HKOs on the other two. 12 HP is to hit a Substitute number, giving a Torrent boost after 3 Subs (which could help if you get a low damage roll on Surf). 140 Spd allows you to outspeed uninvested Tran and Roserade, preventing Will-o-Wisp or Sleep Powder from ruining your fun. The last 104 go into SpD to add bulk, but you can throw some more into speed if you feel the need to speed creep.
As this pokemon is anti-anti-weather, you might want to run some weather to get countered...which, in turn, you counter with this set, if that makes any sense. Rain is the condition of choice, obviously, as only the most specially defensive Tran can stand up to Empoleon's STAB, Rain, and item-boosted Surf, and even then, it just barely does so. The question of Expert Belt vs. Wise Glasses is another power/reliability conundrum, but on a slightly smaller scale than usual - the Belt guarantees Tran is OHKO'd after Rocks damage, while the Glasses ensure that 252/4 Skarm always goes down; with the Glasses, your penalty for missing predictions is slightly softer, while the Belt makes your successful predictions hurt more. You could also run Hydro Pump over Surf to make sure both half-steels go down, but for the most part Surf provides enough power more reliably. Speaking of Stealth Rock, its support is absolutely crucial to this set, breaking Skarm's Sturdy and preventing stalling from turning a 2HKO on Gastrodon into a 3HKO. Grass Knot and Ice Beam 2HKO 252/252+ Gastrodon and Roserade, respectively; the OHKO isn't completely necessary, as those two can't phaze you out on a single misprediction thanks to Substitute.
252+ EB (WG) Empoleon Rain Surf vs 252/4 Skarmory: 91.62% - 107.78% (100% - 117.96%)
252+ EB (WG) Empoleon Rain Surf vs 252/252+ Heatran: 98.7% - 116.58% (90.16% - 106.48%)
252+ EB (WG) Empoleon Grass Knot vs 252/252+ Gastrodon: 59.62% - 70.89% (54.46% - 64.79%)
252+ EB (WG) Empoleon Ice Beam vs 252/252+ Roserade: 64.51% - 76.79% (59.39% - 70.31%)
Heatran's only viable option is Roar and hope for an overprediction, but it's pretty useless in rain anyway. If Skarm can play smart and heal off all Rocks/non-Surf damage, it can tank a Surf thanks to Sturdy and Whirlwind Empoleon out. Gastrodon at +1 always breaks a Sub, but if it gets greedy and goes for a burn you can 2HKO it with minimal risk. Roselia is also a bit of a problem, as even -2 Leaf Storm has a 50-50 shot at breaking your Sub. However, not even a few turns of stalling can stop an Ice Beam 2HKO.
I don't know how much this set is dead weight against teams that don't run Tran/Skarm/Gastro/bulky Grass, but I think being able to combat the current best anti-weather strat with a single pokemon is worth a spot on any rain team. Also, if this set sees any sort of usage, its presence will be a way of keeping these teams honest - try to pull anything to counter this (Earth Power on an otherwise Wall-y Tran, or more SDef investment for Skarm, for instance), and your stalling is weakened against other, more mainstream teams. Try to toggle with the sets in order to counter a standard threat, and your team might become more Emp-weak. Tread with caution, anti-weather.