Okies, lesgo with a Rain stopping trap:
Heatran (M) @ Grass Gem
Trait: Flash Fire
EVs: 252 SAtk / 4 SDef / 252 Spd
Modest Nature (+SAtk, -Atk)
- Magma Storm
- Sunny Day
- Hidden Power [Ice] / Earth Power
As long as Heatran doesn't get dumped on by a Scarf Toed, Heatran is an excellent way to take out Politoed. EVs give as much attacking power as possible so Heatran can beat Specially Defensive Politoed. Sun teams greatly benefit from Heatran, so I recommend a Sun team used around this. Actually, a Sand team could use this as well, as long as your weather starter's still alive. CS teams can also abuse this. Frankly, if you have trouble with Sand teams, you can use this, but it's insanely hard to pull off. Anyways, when a predicted switch into Politoed comes, which is natural, go for STAB Magma Storm to trap it in the battlefield. Get rid of the rain by using Sunny Day, weakening Scald and Hydro Pumps. Then, kill the Politoed off using no charges Grass Gem boosted SolarBeam, which will knock it out. The last slot is mostly filler. Hidden Power [Ice] catches Dragons when they get trapped, and Earth Power deals with opposing Heatran.
Paralysis support is nice on this guy, so a Togekiss or Jirachi would work. Rachi even has U-turn, making it easier for Heatran to come in.
You may also want to go for 140 HP / 252 SAtk / 116 Spd to not be outsped by Specs Toed, max speed, and Will-O-Wisp as the filler to cripple Hippowdon (credit to Enoch-117).