Sign promoting the Celebi Celebration
The Pokémon Fun Fest Celebi Celebration glitch was a glitch reported in Pokémon Gold and Silver. During the Pokémon Fun Fest event in various Six Flags theme parks from August 4th to September 9th 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.