The Celebi Glitch is a supposed glitch in Pokémon Ruby/Sapphire versions that supposedly allows one to capture Celebi.
This Celebi is said to appear usually in Route 123, although there are reports of it appearing elsewhere. None of the glitch's proponents can say exactly what the odds are of finding Celebi, so they just make up something, like "1 in 1,000,000,000,000,000" chance. It is said to be even rarer than Shiny Pokémon.
It is said that the glitch Pokémon ? also appears like this.
Copyright (c) 2003 - 2009 Glitch City Labs Team. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".