God damn it, firehusky beat me to it. No matter though, while I'm going to be using a similar playstyle I plan on using some different Dark Horses.
Pokemon Showdown! Username: WAWFIHA
Prior Hall of Fame Standing: Be gentle, it's my first time
Current Dark Horse Pokemon: Politoed, Kabutops, Omastar, Tornadus-I
Explanation of Dark Horse(s): I've been trying rain offense out a little in advance of this, and it's such a gloriously straightforward and powerful way of playing. Keeping up rain is easy because Ninetales has vanished, Tyranitar is still around but has difficulty switching into rain threats, and asides from the odd Zard Y, which you can handle by playing your Toed carefully, there's really nothing challenging you from controlling the weather in this meta.
Politoed fell hard following the nerf that Gen 6 brought to rain teams, but a lot of people forgot what let this frog run BW OU like the mafia. It has to run Damp Rock now, so it's lost potential both in terms of offensive power and lasting durability, but with Rain boosting its attacks Politoed can still make a splash. Because it's more passive than it used to be because it can't run scarf, specs or life orb any more, a lot of pokes may try to set up on it, but access to Scald and Encore makes this a fool's errand much of the time.
My two big bangers abusing toed's monsoon are going to be the gen 1 fossil duo, Kabutops and Omastar. LO Kabutops is a complete savage, with very little comfortably switching into its rain-boosted Waterfalls. It has Aqua Jet for emergency priority, Stone Edge for a vicious secondary STAB with good neutral coverage, and Low Kick to do a lot to Ferrothorns trying to switch in. Likewise, Specs Omastar absolutely blasts huge portions of the meta for unspeakable amounts of damage, with even bulky resists getting huge chunks of their life bars erased. In rain, both of these make an absolute mockery of OU speed tiers, with only the fastest scarfers managing to outpace them.
Because on a team like the one I've built Politoed's mission is usually suicidal in nature, a backup rain setter is required. For me, that's Tornadus-I, who can set rain back up with Prankster Rain Dance, and in addition its powerful Hurricane provides important coverage against the bulky grass types that might otherwise give my sweepers a hard time. In addition, it has Prankster Taunt in order to run interference against stall, and U-turn to keep momentum.
I really think that due to Drizzle + Swift Swim being unbanned this gen, that rain offense is almost as strong as it was in Gen 5, and is this meta's most unprepared-for threat. I'm really not a good player but I feel with this playstyle I don't have to be to win matches simply because this rain-assisted barrage can be so overwhelming. However, I also know for a fact that there are a couple of threats that can give me problems, and a lot will depend on how prominent they become on the ladder.