Glitch City Wiki:List of unconfirmed glitches
The Pokémon Fun Fest Celebi Celebration glitch was a glitch reported in Pokémon Gold and Silver. During the Pokémon Fun Fest event in Six Flags over Georgia from August 4th to August 12th 2001, there was an event to obtain Celebi called the Celebi Celebration.
From one player's account of the distribution process, a freeze would occur during the distribution if a Pokémon in the party was holding mail. A Nintendo official told the player that he was looking for an item, and asked the player to remove a Spearow named Kenya (likely the Spearow belonging to the NPC Randy)'s mail.
The validity of the glitch is questionable.
The Pokémon Fun Fest didn't just take place in Six Flags over Georgia. It took place in six other Six Flags theme parks too.