Celebi Egg glitch is a thing which some people may not be aware of. Sadly unlike the Mew glitch it is so freaking complex and require you to use the dupe glitch for a bad egg.
More of an unknown feature then a glitch but if you didn't catch any Pokemon and beat Gary/Blue/DICKS/whatever on the 1st gen games before you return to Oak for your dex you can actually get five free Pokeballs.
