I once built a UU Rain Dance team, which was very succesful. Then I thought: 'Maybe it's also this good in OU as in UU.' So I started building an OU team. After I had finished that, it wasn't as succesful as the UU variety, but still good enough to try. So I started fantasising how I could make it better. Eventually, I came up with a very odd lead for Rain Dance, Tyranitar. I worked it out, I tested it and it was succesful. More succesful than the other variant, as this looked like a Sandstorm team at a glance but turned out to be a wickedly fast Rain Dance team. So this is it. It hasn't been fixed yet, but this is just the first version.
Adamant @ Damp Rock
160 HP / 252 Atk / 96 Speed
The odd lead I was talking about. When it enters the field, the opponent will think that it's the lead for a sandstorm team. So, I predict their switch and attack to that, or set up Rain. After that, I will switch to one of my sweepers and start the sweep.
Adamant @ Leftovers
180 HP / 252 Atk / 76 Speed
Ability: Swift Swim
An obvious Pokemon in a Rain Dance team. It can't miss in one. I've chosen for the Double Dance set, as it is ery fast in the rain and immensely powerful. With perfect type coverage, except against Empoleon, it has a very good role in the team as a sweeper and does a hell of a job doing that.
Careful @ Leftovers
252 HP / 40 Def / 216 Sp. Def
Also known as CursePert. If I can't manage to get Sandstorm down, this one comes in as it's immune to Sandstorm. Curse until you get enough and start attacking. Ice and Ground as perfect coverage and Waterfall as second powerful STAB move, even more powerful in the rain. I was considering to drop Waterfall for Rest and switch Leftovers for Lum/Chesto Berry, but I thought a more offensive approach was more useful.
Timid @ Choice Specs
4 Def / 252 SpA / 252 Speed
Hidden Power [Ice]
Revenge killer and powerful sweeper. Thunder instead of Thunderbolt because of the 100% accuracy in the rain. The idea is simple, and it's played simple too. But it's still a good set and a powerful one too. As its ability grants it immunity to a common counter of Rain Dance, it can easily switch in and obliterate the foe. I've changed its Hidden Power type from Grass to Ice, and it works better like this as I now can counter a lot more than bulky waters who are afraid to switch in on this one anyways (except Swampert).
Modest @ Life Orb
4 Def / 252 Sp.Atk / 252 Speed
Ability: Swift Swim
Grass Knot/Energy Ball
The other rain sweeper. With a very dangerous movepool a lot of foes will be taken out. It's good Special attack in combination with its speed are a threat to every opponent. Life Orb of course for more damage.
Timid @ Damp Rock
252 HP / 80 Sp. Atk / 176 Speed
This is another rain dance Set-upper. It also can put up Steath Rock, which is very useful for the team. It has Wish for team support and Thunder because of the accuracy boost in the rain.
Please rate and fix where possible.