Transfer party Pokémon to a new Red/Blue/Yellow game without trades (Generation I)
Read the description for more information:
Warning: This glitch is hard to pull off, and if you reset the game at the wrong time you may corrupt your save file! So I recommend getting a Mega Memory Card or using an emulator and backing up your save first. I don't know if when the save file is 'destroyed' it's possible the Pokémon may actually disappear, but it's probably best to be safe just in case.
This is not my find. I'd like to thanks Addri Trainer for teaching me the exact glitch, Golden Luxray for the 'get all starters glitch' (https://www.youtube.com/watch?v=7WLkP4P2EK4) and MrGlitch for getting two Pikachu (http://forums.glitchcity.info/index.php/topic,6472.msg187736.html#msg187736).
The glitch:
If you do the save corruption glitch (http://bulbapedia.bulbagarden.net/wiki/List_of_glitches_in_Generation_I#Save_corruption, basically reset the game when the Yes/No box disappears but before the text box updates) in Red, Blue, Yellow with an existing save instead of a new game (doing it with no save gives you 255 Pokémon), your new Pokémon will be transferred to the new game, but unfortunately your Pokédex won't be updated, nor will you have your old items so you can't do any expanded item pack glitches or keep items you found useful.
Additionally, you'll lose all badges.
You will still have '0' Pokémon in the Pokédex until you get your starter. High leveled Pokémon may not obey you due to them still having their old ID number (and OT name if you use a different name for your new save).
There is a positive side for the Pokémon not getting registered though. This prevents the prevented progress glitch (https://www.youtube.com/watch?v=OS-v0tGk90g) from happening in Pokémon Yellow, unless you evolve one of the Pokémon you transferred over to your new save.
This glitch is particularly useful for getting HM moves early.