Exp. Charm is an item in the “Gameplay” category (Key Items).
In-game descriptions
| Sword / Shield | A charm that increases the Exp. Points that Pokémon can get. A machine-like object is inside the charm. |
|---|
Where to find it
Not placed on the atlas maps (so far: Red/Blue and Generation 3).
Sources : PokeAPI (items, item_flavor_text, machines) · atlas · pokeemerald species_info.h