How to get a Celebi in gold/silver/crystal using arbitrary code execution

This glitch requires a bit of setting up, and can only be done after getting the coin case and the HM for Fly. To start, put the following items in the following order in your PC storage.

I recommend not having any repeats of items for the ones that can be anything.

Next, you'll want to have your party setup a certain way too. In the first slot, you'll want to have a pokemon that you don't mind turning into a Celebi. It can be anything, but will retain the moveset and name of whatever you choose (which you can adjust later at the Name Rater). In the second slot, you'll want your pokemon that knows Fly. In the third, you'll need to catch a low level pokemon that's never been used in battle (or at least has no stat exp, anything caught near Cherrygrove will work), and finally in the fourth slot you need a Quagsire that's holding an HP UP and has Sleep Talk as its first move.

Now, fly to New Bark Town and take one step into Prof. Elm's lab. Save and reset. Exit the lab, and take four steps to the right.

You should be standing here

Now, open your pokedex and listen to either Machop or Bellsprouts cry. Exit the pokedex, and open your items pack. Switch over to key items (if you don't switch to it the glitch won't work), and use the Coin Case. This executes the code we setup through our party and item storage.

Finally, fly to Goldenrod and deposit the first pokemon in your party (the one that you want to become Celebi) at the Daycare. Take it back and it should have turned into a Celebi!

You can delete illegal moves from the move deleter, and rename it at the Name Rater ^.^

If you want it to have the signature move Heal Bell:

You can either use it in a team that you beat the Stadium 2 Elite Four with to access the move tutor, or you can setup the pokemon you initially turned into Celebi to have it to start. From what I understand, there's only one real way to do the latter, since the only pokemon that learns Heal Bell through level up in Miltank who can only be female and thus can't pass moves down through egg groups.

You can however use a male Smeargle who sketched Heal Bell, but given that there are no pokemon with Heal Bell that you can battle outside of Pokemon Crystal's Battle Tower in the main games, and you can't sketch from link battles, the only option is to have a second gen 2 game cartridge with a Miltank that knows Heal Bell in the party, exchange Mystery Gifts, then battle it at the Trainer House in Viridian City and sketch it from there. It can then be passed onto Snubbull as an egg move, and it will retain this move if you turn it into a Celebi.