Holding a Berry boosts the Pokémon's stats. Which stat is boosted depends on the Berry's flavor.

Made by DrTapeworm. Made for food-related Pokémon. +1 Stat boost and it depends on a berry’s contest category (arbitrary value that might be determined in the item itself):

Cool/Spicy: raises Attack
Tough/Sour: raises Defense
Beautiful/Dry: raises Sp. Atk
Smart/Bitter: raises Sp. Def
Cute/Sweet: raises Speed
Mix: raises one random stat of the above

alternatively, color tag based:
Red: Def
Yellow: Att
Green: Speed
Blue: SpDef
Pink: SpAtt

Might be limited distribution because of balance. We will discuss it eventually.