What acorn makes the gs ball in Pokemon soul silver?

In Pokémon Soul Silver, the GS Ball is associated with the special event involving Celebi. To create the GS Ball, you need to use a specific item called the "Acorn," which is actually a reference to the game's mechanics rather than a direct in-game item. The GS Ball itself cannot be obtained through regular gameplay and was originally introduced in the Pokémon anime series.