Request: "Wild appeared!" (Generation I)
159Read description for more information:
Requested by the TH3S4MUR4I.
"Wild appeared!" is a glitch that was formally cheat only (at least in the English Pokémon games). However, after the discovery of save corruption glitch (from 2008 latest) it became possible to activate it. I also show off an undocumented trick to activate "wild appeared!" that requires Super Glitch.
When you go into a battle and you have 0 (regarded as 256) or a high amount of Pokémon, the enemy Pokémon's name will be corrupted, usually to something that appears blank. Having 249 Pokémon will replace all 10 letters of a Pokémon's name and having 241 Pokémon will corrupt up to the first letter, etc.
But the Pokémon's name isn't the only thing that is affected by "wild appeared!", and the effects depend on the number of Pokémon you have.
53+ Pokémon: Screen changes colour before you send out your Pokémon (I don't know the exact cause).
222+ Pokémon: replaces the music with a sound and usually causes it to stop due to the corruption of the memory address CFC7 (CFC6 in Yellow).
220+ Pokémon: Makes the game freeze in Red and Blue after battle if CFC4 becomes an odd value. But no freeze occurs in Yellow.
239+ Pokémon: 'Mutate' the enemy Pokémon into either Golem, Missingno. (hex:32), Magmar, or Missingno. (hex:33).
This glitch happens because a buffer at $CEE9 (maximum size 6, so $CEEE is the maximum limit) stores data about your party Pokémon 'belt'. $31 is written for no status ailment, $32=status ailment, $33=fainted and $34=empty.
When you have more than 6 Pokémon, the game writes these values to data past $CEEE, causing the glitch, and the values written are apparently based on the data of Pokémon beyond the sixth slot.
(TheZZAZZGlitch's explanation https://archive.today/mJJhM)
Steps:
Save corruption method:
Uses a now well known "SRAM glitch" (video https://www.youtube.com/watch?v=oxuH3damfOU). Saving and resetting early at a very specific time will bring over Pokémon from the old save and update (almost) everything else. If you have no save data and do this, then you can get 255 party Pokémon.
From here, you can get a very limited version of 'wild appeared!' to happen during the first battle with Blue. The only thing you can see happen is having the screen change colour because obtaining Pikachu messes up the party counter.
By swapping the 2nd Pokémon (etc.) with the 10th, you can get 255 items. From here, there are multiple ways to enter a battle without changing your number of party Pokémon from FF, such as using "EtE" (Rival's effect item) or ????? (appears when you stand in a specific spot by Pallet Town's water).
Super Glitch method:
This is method that lets you get 0 or 255 Pokémon, and then any number of Pokémon you want if you have the right Pokémon later.
The actual location used to get 0 Pokémon and the 255 underflow method was found by luckytyphlosion.
Steps:
1) Have a Pokémon with a Super Glitch move as the first move, such as Yellow's Z4 (hex:C3) which learns the move at level 35. Have it learn Super Glitch via Rare Candy in a safe spot (like here http://i.minus.com/ieB2Tly27VDEn.PNG) or level up if you want if you're using Red/Blue and you last opened the Pokémon menu in that spot to prevent a potential freeze.
2) Go to a Pokémon Center just below the PC.
3) View your Pokémon menu and deposit a Pokémon. This will become your number of Pokémon depending on the species' index number later.
4) Press A on the Super Glitch Pokémon to bring up Deposit/Stats/Cancel, but don't deposit it yet. View its moves on its stats menu. There is a chance that your number of Pokémon will become 0, so do this several times to get the 0 Pokémon corruption.
5) If you want, you can walk into the grass and get 'wild appeared!' to happen exactly how it works from the well known "walking into the grass with no Pokémon" cheating method straight away, but you may have a Pokémon that locks up the game. You can do some optional steps below to catch a mutated Pokémon or lower the amount of the corruption:
Optional steps:
5) With the Deposit/Stats box still open, deposit the Super Glitch Pokémon and hopefully you'll get 255 Pokémon.
6) Withdraw a Pokémon to change your party counter to a value depending on the index number of the Pokémon you withdraw. You can use Q/Charizard 'M (FF) if you want to keep 255 Pokémon, otherwise Victreebel (hex:BE, dec:190) is the best option for valid Pokémon.
7) Switch the first Pokémon with the second.
8) Now you can have 'wild appeared!' happen without a lock-up when you try to send out your Pokémon, and you can catch a mutated Pokémon (Missingno. for me) if you have 239 Pokémon or more.