Water type, meaning he gets natural rain territory, whoopee.
Empoleon (M) @ Leftovers
EVs: 136 HP / 68 Def / 252 SAtk / 52 SDef
Bold Nature (+Def, -Atk)
- Stealth Rock
- Hydro Pump
- Signal Beam
- Ice Beam
Because Politoed leads are normally what's setting up your rain, late game rocks are generally amazing in the rain.
Hydro Pump is STAB and powered up in the rain, while Signal Beam and Ice Beam are coverage, simple, huh?
Empoleon (M) @ Choice Band
EVs: 4 HP / 252 Atk / 252 Spd
Adamant Nature (+Atk, -SAtk)
- Aqua Jet
- Drill Peck
Here we go! Choice band is immediate boosting, and Aqua Jet is priority, rain boosted, STAB boosted, AND Choice band boosted!
That's some sick nasty power! Waterfall, Earthquake, and Drill Peck are all just fillers really, the " If he can actually outspeed something " fillers. But yeah, that's it.
Overall, he gets boosted STAB, but that boosted STAB helps him a lot!
Rating for the rain - 5.5/10