This Scolipede is a poison-type Pokémon owned by Roxie.
After Koffing was defeated, Roxie sent her Scolipede, who resisted Leavanny's Razor Leaf move and badly poisoned him with Toxic.
Leavanny tried to attack Scolipede with Energy Ball, but missed. Instead, Scolipede attacked Leavanny with Rock Tomb and Sludge Bomb, defeating Leavanny. Ash sent his Pignite, who started with Flame Charge, but was stopped by Scolipede's Screech. Scolipede tried to attack Pignite with Sludge Bomb, but the attack was negated by his Flamethrower. Scolipede was hit by Flame Charge, but dodged Pignite's Flamethrower and poisoned him with Toxic. Fortunately for Ash, Pignite managed to defeat Scolipede in an instant, using Fire Pledge.