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One that is rumoured to happen is that Ruby cartridges have a 1/1000 chance of finding a Celebi in Route 121 (the one before Lilycove amrite?). It became popular in Nintendo's forums, and there are a few videos. Though I have no proof to wheither that is real or not.
A thread for spreading common misconceptions doesn't seem like a very good idea to me. Anything that includes getting an event Pokémon without going to an event is obviously fake and if you can't find the "Secret" on a reliable Pokémon site, don't waste your time trying it out. Using common sense never hurts either.