Here's the poliwrath set I run
Poliwrath @ leftovers
Trait: Swift Swim
40 Hp/252 def/216 speed
Jolly nature
Belly Drum
Waterfall
Brick Break
Encore
The key here is survivability. In the rain, the wrath hits 506 speed, which is enough to outspeed max speed deoxys-s. Timid/Jolly scarfed base 100 pokemon are out of your speed range, so there is no reason to max speed. The max defense allows belly drum to become much easier to set up. With this EV spread, wrath tanks 252 Jolly Doryuzzu's Earthqauke AFTER using belly drum. Losing less than half your life after a STAB base 100 attack from a pokemon with base 135 is enough to warrant the defensive spread if you ask me. You aren't running any attack EVs but who cares? You're maximizing your attack ala belly drum. Putting 252 EVs into your attack is just overkill.
After a belly drum, this set handles almost all common threats. Nattorei is OHKO'd. Every single non uber offensive dragon not named dragonite is KO'd. Mence and bulky gyara(!!!) die to your +5 boosted attacks. The other intimidate pokemon aren't living through waterfall or Brick break. Skarm and Blissey also fall. 252/252 bold suicune is 2HKO'd by Brick Break with or without rocks. This thing is just amazing. Leftovers means that you aren't just a suicide pokemon and poliwrath will be able to sweep both mid game and late game (although you'll still want to wait until late game to dispose of theats). You're resistant to Scizor's u-turn and bullet punch and you aren't 2HKO'd by bullet punch either when factoring in belly drum. Encore is filler, but can be quite useful against bulk up roobushins and other pokes who wish to set up against you.
Deliberately, this set loses to burungeru. Why? So that ditto can't switch in on you and tear you limb from limb. Unless you want to live in fear of that thing switching in on you and gaining your +6 boosts, swift swim, and scarfed attacks, carry burungeru or pay the price.
Things to watch out for are every last mischievous heart pokemon in the game. Sableye will-o-wisps. Murkrow uses confuse ray or haze. Erufuun uses Stun spore(or if you're me, worry seed for a guarenteed end of sweep). The electric genie, illumise, and volbeat also carry thunder wave. Thanks to sashes and sturdy pokes, this set absolutely needs rocks up to live. Red card is no friend of yours either. I haven't done calcs for parasect or toxicroak. But if people haven't realized how dangerous lanturn is to most rain teams, they won't carry toxicroak either.