Hey alexwolf, here's the analysis to Specs Rotom-H that I wrote (if there are any errors, fell free to correct them, as I am not an english expert):
[SET]
name: Choice Specs
move 1: Volt Switch
move 2: Overheat
move 3: Thunderbolt
move 4: Trick / Hidden Power Ice
item: Choice Specs
nature: Timid / Modest
evs: 4 HP / 252 SpA / 252 Spe
[SET COMMENTS]
<p>Rotom-H can also forgo all its defensive ideals, and instead become a powerful lure and wallbreaker. Unfortunately, Rotom-H's selection of moves and middling speed mean that it is not going to sweep anytime soon, not to mention its extreme weakness to Stealth Rock. Still, this set should not be understimated, as even Chansey loses at least half of her health if she dares switching-in on a sun-boosted Specs Overheat. While this set initially appears to be outclassed by Heatran, the latter lacks a way to mantain momentum and an usable secondary STAB, has problems dealing with bulky Water-types, and is threatened by Dugtrio. Rotom-H doesn't have these problems; this should be sufficient to separate him from Heatran.</p>
<p>Volt Switch is a useful scouting tool that is also extremely powerful against bulky Water-types. Overheat, when boosted by Choice Specs, STAB and Sun, is exceedingly powerful, and destroy anything that doesn't resist it (and some things that do) and is not named Chansey or Blissey. Thanks to Volt Switch and Thunderbolt, bulky Water-types, especially Politoed, must think twice about coming in to absorb Overheat. Speaking of Thunderbolt, it is the other main option that is used over Volt Switch when you don't want to switch. Rotom-H generally doesn't need more coverage than its STAB offer, thanks to Overheat's godly power under sun. Thunderbolt also allows Rotom-H to 2HKO offensive Heatran after Stealth Rock damage. Trick is the option on the last slot; even though the pink blobs take a lot of damage from Overheat, it is still not sufficient to 2HKO them, so Trick is used to surprise and cripple both for the rest of match. Hidden Power Ice can be used instead, as it OHKOes Garchomp, Dragonite without Multiscale and pressures Latias more effectively than Overheat, since Roost stalling will be very difficult.</p>
[ADDITIONAL COMMENTS]
<p>Rotom-H absolutely hates Stealth Rock, especially considering that its main STABs force him to switch a lot, so Rapid Spin or Magic Bounce support is a must. Xatu stands out as a partner due to its ability to toxic stall Chansey and Blissey, two pokémon that are still headaches for Rotom-H to deal with. Xatu also has U-Turn, which forms a Volt-Turn combo with Rotom-H. Ninetales is also an essential, as it's the eternal sun that makes Overheat so powerful and hard to switch into. If you aren't using a sun team, you are probably better off with Rotom-W, or even Rotom-C, as neither of them are weak to Stealth Rock, and the former has a much more reliable STAB than Overheat.</p>
<p>Due to Overheat being extremely powerful on its own, there aren't much other viable options that Rotom-H can run. Other Hidden Power can be considered, but remember that a neutral sun-boosted Overheat outdamages even a 4x super-effective Hidden Power, and most of time even if the target resists Overheat, that move is sufficient to do the job. Hidden Power Fighting can be considered against Tyranitar. It 2HKOes all positively-natured 252 HP/192 SpD versions, and other versions are 2HKOed regardless. It has little use outside that, though. In the same vein, Hidden Power Ground can be used against Heatran. Thunderbolt only 2HKOes versions that don't invest on Special Defense, while Hidden Power Ground 2HKOes even the most specially bulky of Heatran. But again, it has no use outside that, and you are better off using a partnered Dugtrio. Hidden Power Grass is a nasty surprise against Gastrodon, but other Water/Ground-type Pokémon like Swampert and Quagsire are 2HKOed by sun-boosted Overheat anyway.</p>
<p>Dugtrio and Terrakion stand out as great partners to Rotom-H. The former traps three things that are headaches for him: Tyranitar, Heatran and opposing Terrakion. A Rotom-H with Trick can even remove Shed Shell, Choice Scarf or Shuca Berry from those threats, all items that prevent Dugtrio from effectively trapping them. With Dugtrio removing the aforementioned Pokémon, Rotom-H can freely spam Overheat. Terrakion cannot trap things, but it is much more powerful, can defeat the pink blobs, and can open holes on the opponent's team that Rotom-H can later take advantage. Another great partner is Genesect, a Pokémon that can form a Volt-Turn combo with Rotom-H thanks to STAB U-Turn.</p>