While Rotom has a shallow attacking movepool, it has just enough options to make effective use of a Choice item. With immunities to Spikes and Toxic Spikes, as well as a neutrality to Stealth Rock, Rotom can switch in and out many times while taking minimal damage. However, this is not the only factor that makes Rotom's Choice sets very effective: when equipped with a Choice item, Rotom becomes a very potent threat. With a Modest nature and a Choice Scarf, Rotom reaches a Speed stat of 421, while Timid Choice Specs Rotom attains a sky-high Special Attack stat of 433.
Aside from being a solid STAB attack, Volt Switch is an excellent momentum-grabbing move, which racks up damage and scouts the opponent's switch-in. Thunderbolt is another option for greater power, and can grant Choice Scarf Rotom an easier endgame sweep. However, be careful about recklessly using either of these moves, as Ground-types and Pokemon such as Volt Absorb Jolteon, who are immune to Electric-type moves, will leave Rotom no choice but to switch out with its metaphorical tail between its legs. Shadow Ball, Rotom's secondary STAB attack, has good synergy with its Electric-type STAB, as few commonly seen Pokemon resist both moves. Rounding out Rotom's arsenal, Hidden Power Fighting grants unresisted coverage alongside Rotom's dual STAB, hitting Steelix, Magneton, Krookodile, and the rare Ferroseed super effectively. Despite being super effective, however, even Choice Specs Hidden Power Fighting will scarcely dent the likes of Snorlax, hence the last move, Trick. With a little prediction, this nifty move can easily render most walls and bulky Ground-types, such as Gligar and Quagsire, virtually useless.
Hidden Power Grass can replace Hidden Power Fighting to surprise the aforementioned bulky Ground-types, Rhyperior in particular, but Trick often deals with them just as effectively. If choosing Hidden Power Ice, Rotom should also utilize Choice Scarf and a Timid nature in order to revenge kill Adamant Choice Scarf Flygon and all Choice Scarf Nidoking. Maximum Speed investment also allows Choice Scarf Rotom to outspeed all +2 Gorebyss and neutral-natured +1 Sharpedo, making it an option worth considering if these threats are troublesome. On the other hand, a Modest nature gives all Rotom a much-needed boost to its unremarkable base 95 Special Attack. Discharge and Thunder are alternative primary STAB moves, but the former's power drop is undesirable on an offensive Rotom, while the latter's accuracy is poor outside of rain, and there are better Rain Dance abusers out there. Finally, Will-O-Wisp, though odd on a Choice set, may be useful to cripple physically based Ground-types who switch in looking to catch Rotom locked into Volt Switch, if Trick isn't your cup of tea.
While Rotom's three attacks have excellent coverage together, neither of its STABs are particularly good attacking types to be locked into: the numerous Ground-types in UU, such as Rhyperior, Flygon, and even Nidoking, laugh at Thunderbolt and Volt Switch, and thanks to their high offensive stats, can pose a significant threat to your team. Normal-types, particularly Snorlax and Clefable, take no damage from Shadow Ball and can retaliate with crippling status or a super effective Crunch; Dark-types, such as Weavile, Bisharp, and Krookodile can also switch into Shadow Ball and decimate Rotom with a powerful STAB Pursuit. There are many ways to handle the individual Ground-type threats; bulky Water- and Grass-types, such as Slowbro, Suicune, Roserade, and Shaymin, generally fare well. Fighting-types, such as Hitmontop, Machamp, and Heracross, are good options to help your team counter the latter threats, but Rotom must tread carefully so as to avoid eating a boosted Pursuit.