Rain Dance Jolteon
@life orb/damp rock
4HP/252 SpA/252 Spe
Timid
-Rain Dance
-Substitute
-Thunder
-Hidden Power (Water)/(Grass)/(Ice)
This set is designed to come in on an enemy that will be forced out such as gyarados, suicune, vaporeon, or really any other slower, frail sweeper such as gengar or infernape. Or, ideally, jolteon's electric immunity to nab some free health too. The idea is to throw up a sub on that pokemon and either hope they switch or try to status you. The sub will block those two, but even if they attack, it's not the end of the world. All of these pokemon can be dealt with with the appropriate move. Once the sub is up, you proceed to rain dance and devastate the enemy with STAB LO thunders from jolteon's massive special attack.
Hidden power water is for the boost in rain and great nuetral coverage. You essentially have a 105 base power move with fantastic coverage. Great partner to steels who appreciate the loss of a fire weakness, offensive suicune who gets essentially a free calm mind boost, and any other team with flying, electric, or fire type weaknesses. The hidden powers are all interchangeable for your specific needs. Highest base power goes to water, the ability to nail swampert hard is grass, and the best nuetral coverage is ice. Ice also keeps you from being walled by breloom, an increasingly common threat. A mention should go to hidden power fighting because if you are behind a sub, you will be able to outspeed all forms of tyranitar and 2hko. This can be a huge help because it not only allows jolteon to have a full power, 100% accurate thunder, but if you are using jolteon on a rain team, it helps eliminate a huge pain for weather teams
Toxic spikes support from forretress or roserade is highly recomended in order to have an easier time wearing down enemies such as blissey and swampert. Which, naturally, makes agility sub petaya berry empoleon a great sweeping partner because this jolteon can support with rain and punch holes in the usual counters. I say roserade/forretress and leave out tentacruel (my favorite toxic spiker) because they both greatly benefit from rain while tenta already doesn't mind fire attacks. Also, he shares a ground weakness with jolteon.
EDIT:This is also pretty much a surefire counter to standard zapdos, being immune to it's main form of offense, and buying a free resistance to it's second option, heat wave
And this set deals upwards of 55% to damage to breloom with thunder and is very likely to 2HKO with rocks so hp ice is a little less important