Skill Booster

Skill Boosters (separate from the Enhancements Skill Boosters S/M/L), also known as Personalized Skill Boosters (PSB), are an item introduced in the recent 3DS v1.3.10 update and Mobile v1.6.4 update. They are usually rewarded as Drops during certain Special Stages (the event notes will specify). However, unlike other rewards, these Skill Boosters are immediately used on that specific Pokémon, increasing its Skill Gauge by 1.