Quoted By:
>In Generation I (when the item was known as the Exp.All in English), if it is in the Bag, Exp. All halves the experience and stat experience earned by the player's Pokémon that participated in the battle in order to distribute experience and stat experience to all party members.
>Half of the earned experience and stat experience is distributed evenly among party members who participated in the battle. Then, due to a bug
Sometimes I'm impressed Game Freak managed to make a billion dollar franchise empire considering they could barely make a functional game
