Copy/Pasting this from the sunlight thread:
Genosekuto @ Life Orb
Rash or Mild/Download
6 ATK/252 SpATK/252 SPD
- U-Turn
- Thunder
- Hidden Power Fighting
- Flamethrower/Nitro Charge/Ice Beam
The whole purpose of this starter is to wreck opposing weather starters while having a chance to U-Turn to an appropriate counter, or Ninetales to invoke sunlight again if necessary.
Politoed
Thunder deals 66.1% - 78.1% to Politoed with a 252/252 Calm spread, and will be 100% accurate while in the rain, along with 30% chance of paralysis. Because Politoeds Special Defense is much higher than its Defense, Genosekuto will gain the download boost for Attack, dealing 56.5% - 66.7% from U-Turn. If for some obscure reason Politoed doesn't have higher Special Defense on its spread and Genosekuto gains the Special Attack boost, Thunder is an instant KO.
You are given 3 scenarios:
1) Politoed is dealt a minimum of 66% damage from Thunder + possibility of paralysis. From there, it proceeds to switch while you U-Turn, dealing damage to the incoming thread and switching to a counter of your choice, or Ninetales to start Drought.
2) The same scenario plays out as scenario 1, except Politoed stays in and subsequently faints. From there, Politoed is no longer able to effect the weather, and you can switch to Ninetales and proceed to win.
3) Your opponent switches immediately upon seeing Genosekuto, and worse case scenario the incoming threat is immune to Thunder. From there, simply U-Turn out and switch to appropriate counter or Ninetales to start the sunlight and switch the momentum in your favour.
Tyranitar
Note: If someone could please inform me on how Download properly works if I am incorrect in my assumptions, I'd appreciate it. I am unsure as to whether or not Download takes in to account Tyranitars Special Defense boost from the sand and being a Rock type, or if it just uses the raw stats. I'm assuming the latter. Either way it doesn't matter too significantly because the end result is ultimately the same.
Assuming a 252/252 Careful Spread in the sand (which is what I use to keep Tyranitar alive), Hidden Power will deal 49.5% - 58.4% to Tyranitar. Given that Genosekuto will receive the Attack download boost in this case, U-Turn deals 79.2% - 93.6%.
If for some reason Tyranitar is running a more standard spread for a lead, Genosekuto will receive the download boost for Special Attack, and will almost always be a direct KO. Even assuming a 252/252 Careful spread against the download boost (which isn't possible, but just for figures), Tyranitar would receive 73.3% - 87.1% while proceeding to be hit with 79.2% - 93.6% damage on a 252/0 Neutral Nature Tyranitar via U-Turn.
The point is that regardless of what spread the Tyranitar is running, HP Fighting + U-Turn will 2HKO Tyranitar, while just using U-Turn by itself will often yield a lot of damage. It also has the same benefits as dealing with Politoed did in that it allows you to switch to an appropriate countermeasure or Drought Ninetales.
I'd also like to point out that Download is a great way in helping you assess your opponents set, as it will give you a estimate to where the EV spread lies.
Hippowdon
Put simply, Ice Beam is a OHKO under most instances. If for some silly reason Hippowdon is running a bulkier Special Defensive set and Genosekuto doesn't receive the Download boost, which is possible, it will take 59% - 69.5% from a 252/252 Careful spread from Ice Beam anyway, a clean 2HKO. It's also worth mentioning that a 252/0 Careful spread on Hippowdon for physical defense takes 35.7% - 42.1% from a Download boosted U-Turn, which combined with Ice Beam, is a very high probability for KO. If someone could calculate that for me, that'd be cool.
Mind you, if you choose to use Flamethrower for difference in coverage + abuse the sunlight boost (or Nitro Charge) you won't be able to deal with Hippowdon using this set.
Abomasnow
If you're running Flamethrower, President Snow dies immediately. That said, it is more than likely going to get the boost for physical attack by Download and will OHKO with U-Turn anyway. This would likely be the wisest decision given that I can't imagine an Abomasnow staying in against a Genosekuto, and if you're carrying Ice Beam it is your best alternative. Even if Abomasnow ran some weird EV spread that involved 252 HP EV's and a balance that allowed it to carry higher Defense and subsequently avoid a boosted U-Turn, it will still take 68.8% - 81.3%. It's hardly even worth mentioning though.
EV's on the spread are simplistic, yes. However I didn't feel like lowering Speed if only for the fact that it allows Genosekuto to outrun maxed out Sanzadora and Ononokuso, and the Special Attack EV's are necessary to run the set. I'm sure it might be possible to lower the Special Attack EVs down in favour of strengthening U-Turn, but I'm lazy now and will look in to that later.