Washed up former great
Due to Rotom-H's great typing, ability, and defensive stats, it can check a large number of top-tier threats such as Mega Scizor, Thundurus, Kyurem-B, and most Landorus-T variants. It has resistances to Electric, Fire, Bug, Steel, Flying, and Ice and an immunity to Ground, which are all common attacking types in STABmons. It can also function as a status sponge because it is immune to Thunder Wave and Will-O-Wisp. Rotom-H can support its team with a variety of status moves and can also keep up momentum with Volt Switch; additionally, it has access to high-Base Power Fire-type moves such as Blue Flare, Eruption, and Searing Shot. It is very versatile and can be used on a variety of teams. On the other hand, Rotom-H lacks good coverage moves and reliable recovery. It also faces competition from Rotom-W, which has a better overall defensive typing. Its below-average Speed stat forces it to use a Choice Scarf to compensate for it or else be outsped by threats, and its poor HP stat doesn't allow it to take as many hits as you would like.
name: Specially Defensive
move 1: Volt Switch
move 2: Lava Plume
move 3: Nuzzle
move 4: Pain Split
evs: 252 HP / 4 Def / 252 SpD
Volt Switch allows Rotom-H to maintain momentum and switch to a teammate with a better matchup against the foe. Lava Plume has a 30% chance to burn the foe, which can be important to cripple physical attackers. Nuzzle has a 100% chance to paralyze the foe, which is very useful to slow it down and cripple it for the duration of the battle. Pain Split is Rotom-H's only real form of recovery, and because of its low base HP, it can often use the move to regain health while damaging the foe. Searing Shot also has a 30% chance to burn the foe; however, it hits harder than Lava Plume at the cost of having much lower PP. Blue Flare is another option for a Fire-type STAB move that hits harder but has low PP, below-average accuracy, and a lower burn chance. Will-O-Wisp is an option to inflict a guaranteed burn on the foe.
Levitate makes Rotom-H immune to Ground-type moves, turning what would be a 4x weakness into an immunity. Leftovers allows Rotom-H to passively recover HP each turn. Because Nuzzle isn't meant to deal significant damage, a Calm nature is run to make Rotom-H as bulky as possible, and Attack is the only stat it doesn't mind the drop in. Maximum EVs in HP and Special Defense help to make Rotom-H as bulky as possible, especially in conjunction with the Attack drop from a possible burn. Rotom-H can also run maximum Defense EVs and a Bold nature to tank hits better from stronger physically attacking foes.
Pick which status move to use on the foe. If Rotom-H is facing a fast foe that gives your team a Speed disadvantage, try Nuzzle. If facing a physical attacker, try Lava Plume for the burn chance. Pain Split works based on Rotom-W's raw HP number, not its percentage, so don't accidentally weaken Rotom-W and heal a foe that may have a higher HP percentage and a lower overall HP stat than it. Use Volt Switch to pivot into something that will force a switch and either let a teammate set up on the foe or simply beat the foe one-on-one. If using Searing Shot or Blue Flare, be careful with PP and try to save them. Because Rotom-H's Speed stat isn't great, don't be afraid to switch out manually if the opponent brings in a Water- or Rock-type that is faster than it.
Water-types such as Mega Blastoise, Azumarill, and Gyarados make for good switch-ins to other Water-types and hit Fire- and Rock-types hard with super effective STAB moves. In return, Rotom-H is able to take the Grass- and Electric-type moves that they don't like. Keldeo resists Water- and Rock-type attacks, and Rotom-H is able to take the Flying-type moves it doesn't like. Grass-types are also able to hit Rock-types as well as Water-types with super effective STAB moves. Other VoltTurn staples such as Landorus-T, Tornadus-T, Scizor, Thundurus, and Parting Shot Sableye work well to keep up momentum and continually switch out of the foe. Entry hazard setters such as Landorus-T, Heatran, Ferrothorn, and Garchomp work well due to their ability to help wear the foe down over the course of the battle along with any possible burns that Rotom-H inflicts. Entry hazard removers such as Landorus-T, Gyarados, Porygon2, and Skarmory are able to keep the field clear of hazards, which Rotom-H appreciates because it switches in and out often.
name: Choice Scarf
move 1: Volt Switch
move 2: Blue Flare
move 3: Thunderbolt / Eruption
move 4: Trick
item: Choice Scarf
evs: 252 SpA / 4 SpD / 252 Spe
Blue Flare is Rotom-H's primary Fire-type STAB move that hits hard but has below-average accuracy. Volt Switch allows Rotom-H to hit the foe and then switch out to maintain momentum. Thunderbolt is an option for a secondary STAB move that hits harder than Volt Switch and doesn't force Rotom-H to switch out. Eruption hits incredibly hard because this set normally goes first; however, it doesn't always deal massive damage due to the amount of Fake Out + Extreme Speed users in the metagame. Trick serves as a way to cripple foes on stall teams by locking them into one move for the rest of the match. Searing Shot is an alternative STAB move that has 100% accuracy, has a 30% chance to burn the foe, and hits hard, but it has fewer Base Power than Blue Flare. Hidden Power Ice is a good option to hit Ground-types such as Landorus-T and Garchomp hard when they switch in on a predicted Volt Switch.
Levitate removes the weakness Rotom-H would have to Ground-type moves, allowing it to freely switch into those moves. Choice Scarf allows Rotom-H to outspeed many threats in the metagame. A Timid nature and maximum EVs in Speed and Special Attack serve to make Rotom-H as fast and strong as possible.
With Heatran being extremely popular and immune to Fire-type moves, and with Ground-type foes being immune to Electric-type attacks, Rotom-H's STAB combination is a risky one to be Choice-locked into, so prediction is key. This will also give Rotom-H a lot of problems breaking down bulky foes. Many times, when facing a bulky foe such as Chansey, it is better to either Trick Rotom-H's Choice Scarf onto them or pivot out with Volt Switch into a teammate that can handle them better. Don't lock Rotom-H into Trick when your opponent has their Mega Pokemon on the field or you suspect they will switch to it. This gives the foe a free setup opportunity and can also lead to it inflicting a lot of damage on your team. Beware of all the Fake Out + Extreme Speed users and other priority users, as they obviously make Rotom-H's Choice Scarf useless. This set also has the added bonus of surprise factor, which allows it to revenge kill many unsuspecting foes particularly when the opponent leaves their Pokemon in, expecting it to outspeed Rotom-H.
Wallbreakers such as Keldeo, Mega Scizor, Thundurus, and Ursaring are able to take care of bulky foes that give Rotom-H trouble. Counters to priority users, such as Will-O-Wisp Sableye, Tyranitar, and Ferrothorn, can stop them from damaging Rotom-H before it can move. Entry hazard setters such as Garchomp, Heatran, and Ferrothorn are able to damage the foe over the course of the battle, which can help Rotom-H have an easier time KOing them. Entry hazard removers such as Landorus-T, Rapid Spin Porygon2, and Skarmory are also good partners, as they let Rotom-H switch in freely multiple times. VoltTurn staples such as Landorus-T, Parting Shot Sableye, and Thundurus are able to keep up momentum by switching to keep the foe on their toes and maintain offensive pressure.
Toxic can be run to wear down bulkier foes. Sleep Talk can be run to let Rotom-H absorb almost every status, allowing it to counter all Grass-types, including Spore users. Magma Storm could be run alongside Toxic to trap foes on stall teams and wear them down quickly; however, this is better used by Heatran because Rotom-H doesn't learn Taunt, so it cannot prevent them from healing. A RestTalk set could be used, but counting on Sleep Talk is not reliable. Choice Specs can also be used, as it allows Rotom-H to hit incredibly hard.
Checks and Counters
**Fast Water-types**: Fast Water-types such as Choice Scarf Keldeo, Starmie, and Water Shuriken Azumarill are able to outspeed and heavily damage, if not OHKO, Rotom-H.
**Rock-types**: Rock-types such as Terrakion, Aerodactyl, and Tyranitar give Rotom-H a lot of trouble, as they resist Fire and are able to hit back with super effective STAB moves.
**Wallbreakers**: Wallbreakers such as Ursaring, Mega Lopunny, Adaptability Porygon Z, Mold Breaker Excadrill, Mega Gyarados, and Earth Power Kyurem-B can give Rotom-H problems by just overpowering it.
**Bulky Special Walls**: Bulky special walls such as Chansey, Porygon2, and Meloetta are able to heal off the damage and status ailments that Rotom-H causes, and it is not able to inflict significant damage on them.