Overview
With the highest Special Attack in the tier Slugma sets itself apart from the other Fire type Vulpix thanks to its Sp Def boosting potential with Amnesia and a higher Sp Atk. stat.

Although due to its low speed and only decent bulk, Slugma usually finds itself being forced to take a hit before it can attack and often cant be switched in on many attacks either.

However if played correctly and kept healthy Slugma is a dangerous and great offensive threat many teams may not be ready for.

Offensive
Slugma @ Chesto Berry/Leftovers
Ability: Flame Body
EVs: 252 HP / 4 Def / 252 SpA
Modest Nature
IVs: 2 Atk / 30 SpA
- Fire Blast
- Hidden Power [Grass]
- Rest
- Amnesia/Sleep Talk

Set Details:
Fire Blast is Slugma's best stab option as there are very few Pokemon in the tier that aren't Ohkod or 2hkod. Fire Blast Ohkos Seedot, Nincada, Spinarak, Sunkern, Slakoth, Poochyena, Pichu, Tyrogue, no investment Ralts even after a Calm Mind, and Sentret. Fire Blast also 2hkos max Igglybuff, as well as Cleffa 50% of the time. Hidden Power Grass Ohkos Feebas and at least allows Slugma to hit Seel. Amnesia allows Slugma to boost its Sp Def to allow it to take Special Attacks better allowing it to not be Ohkod by Feebas' and Seel's Surf, and take Ralts' Psychic and Pichu's Volt Tackle better. Finally Rest + Chesto Berry allows Slugma to heal back to full and have a chance at 2nd life, alternatively Slugma can run Sleep Talk to attack while asleep but this is dangerous due to being unable to control what move Slugma will use.
Max Hp Maximizes Slugma's Bulk allowing it to take some strong hits like +1 Tyrogye HJK and Max Sp Atk maximizes Slugmas offensive power. Flame Body is used over Magma Armor for Burn chances against Physical Attackers.

Other Options:
Slugma can run a Quiet nature with Rock Slide to 2hko Vulpix and Hoothoot, but struggles to find the room for it.
Toxic can be used for Seel switchins, and Yawn can be used to force switches.

Checks/Counters:
Seel/Feebas: Feebas outspeeds and Ohkos with Surf, unless Slugma has an Amnesia up then Slugma can ohko with Hp Grass. However Slugma cannot do much of anything to Seel.

Vulpix: Unless Slugma is running Rock Slide or Toxic Vulpix hard walls Slugma in everyway.

Strong Attackers that outspeed Slugma: while they cannot directly switch in they can easily revenge kill a weakened Slugma.