X Sp. Atk
From Pixelmon Wiki
An X Sp. Atk is a type of medicine that temporarily raises a Pokémon's Special Attack by one stage while in battle. It can be obtained from shopkeepers and as a tier 1 special drop.
Crafting
X Sp. Atk can be crafted by using a Salac Berry in a Brewing stand when supplied with 1-3 water bottle(s).