Moves
Slack Off lets Slowking wall Keldeo, Latios, Alakazam and Reuniclus. Scald is Slowking's best offensive move option due to its ability to cripple Ferrothorn, Skarmory, and bulky Water-types. Dragon Tail lets Slowking phaze Pokemon that can try to set up on it, like Calm Mind Reuniclus and Latios. Alternatively, Ice Beam is Slowking's best option to not be setup bait for Substitute users like Dragonite, Garchomp, and Breloom while still pressuring Latios and specially defensive Gliscor. Fire Blast is mainly for Ferrothorn, which can otherwise use Slowking to stack Spikes. It also nails other Grass-types like Celebi and Breloom. However, Psyshock is an option that lets Slowking damage Water-types, especially Keldeo, Jellicent, and Tentacruel, while also hitting Terrakion and defeating Toxicroak, Amoonguss, and Breloom. Finally, Thunder Wave keeps dangerous setup sweepers like Quiver Dance Volcarona in check while crippling other fast threats like Alakazam, Latios, Keldeo, and Tornadus for Slowking's teammates. While Dragon Tail + Ice Beam is also a viable option, this combination requires specific support to work considering it leaves Slowking exploited by Water-types and Ferrothorn.
Set Details
252 HP with 180 Special Defense EVs alongside a Calm nature let Slowking avoid a 2HKO from Choice Specs Keldeo's Hydro Pump in rain after Stealth Rock and avoid an OHKO from +1 Volcarona's Bug Buzz without entry hazard damage. An alternative spread of 252 HP / 232 Def / 24 SpD with a Calm nature can be used to improve Slowking's general utility and still take Substitute Thundurus-T's Thunder while not being 2HKOed by Mamoswine's Earthquake and reducing Pursuit damage. However, this spread leaves Slowking unable to check Volcarona or Choice Specs Keldeo in rain if Stealth Rock is up. A Bold nature can also be considered because it makes it easier to take Tyranitar's Pursuit and other physical attacks from Pokemon like Gliscor, Mamoswine, and Garchomp while still being able to take on threats like Keldeo, Alakazam, and Latios.
Usage Tips
Use Slowking to wall strong special attackers like Keldeo, Latios, and Alakazam, and use Slack Off as soon as its HP drops below 67% because it usually needs to be at full health to safely check those Pokemon. Spam Scald early-game to burn Pokemon that can otherwise freely switch into Slowking, like Ferrothorn and Rotom-W. Be smart with when you use potential coverage moves because it's the surprise factor that will make them work most of the time. If using Psyshock, Ice Beam, or Fire Blast, only reveal them when you're sure Slowking will get the KO or permanently cripple its targets. Use Dragon Tail if a Pokemon that can normally use Slowking as setup fodder enters the field, like Reuniclus, Latias, or Volcarona, and if Spikes is up, as Slowking can force a lot of switches. Avoid getting Slowking statused, since burns and poison make it easier to KO and paralysis can keep it from using Slack Off.
Team Options
Slowking is vulnerable to all entry hazards, so using it alongside Rapid Spin support is a must. Because of this, its best partner is Mold Breaker Excadrill, which can also deal with Slowking's Electric-type weakness and even defeat Rotom-W. Pokemon that can switch into Rotom-W and other Electric-types like Latios, Poison Heal Breloom, Amoonguss, and Celebi are important partners. Slowking also loves to be paired with Tyranitar because it can remove Reuniclus, one of Slowking's biggest problems, while setting up sand to help it defeat rain structures and helping Slowking check Latios. Other Pursuit users like Scizor and Weavile are also usable. Slowking needs entry hazard support to be used effectively, especially Spikes, so Ferrothorn or Skarmory is strongly recomended. Other Stealth Rock users like Landorus-T, Gliscor, Garchomp, and Heatran are also very good choices. On the offensive side, Pokemon that can help with setup sweepers that Slowking can't deal with are appreciated. Choice Specs or Choice Scarf Latios is an awesome partner because it can check Thundurus-T and cripple setup Pokemon with Trick. Choice Scarf Garchomp can check Volcarona and help against Thundurus-T and DragMag teams. Dragonite can also be used to check Volcarona and revenge kill setup sweepers with Extreme Speed, but it isn't quite as good on sand teams. Mamoswine can deal with weakened Thundurus-T and Dragon-types with Ice Shard and loves Slowking's defensive support. Magnezone can trap and remove the two most common Spikes users, Ferrothorn and Skarmory, while pressuring Excadrill if using Choice Scarf or Air Balloon.