Arbitrary type capture manipulation (powerful faster than Rival LG, longer to set up) (Generation I)
Notes: This glitch utilizes arbitrary type name 0x4F, which gets its name from FA7E (just before the box Pokémon at DA80/DA7F). See my previous video about this https://www.youtube.com/watch?v=6V6F-mtkFTc .
We acquire arbitrary type name 0x4F from the TM03 glitch move. A list of glitch Pokémon that learn it can be found here. https://glitchcity.wiki/AttackDex/Y:203
It should be able to work with 0x50 too, but is harder. Setting up arbitrary code execution may not be needed as a specific set of box Pokémon may work. This glitch may take a long time to set up without a modified save, but is faster than Rival LG.
You'll need:
DA7E (85) d:46 x $52 80 53 50 ; or a variation of two normal characters, 46 $52 bytes, one $53 byte and one $50 byte at the end.
Player name: 6 (single length) characters long
D349 (rival name) 01 xx 50 (any two single length characters, last one you modify with species ID; it's a quantity in the expanded inventory. The 01 set up makes it a Master Ball. It can be another item that is consumed in battle too without ending it e.g. Poké Ball or Potion)
Method:
1. Scroll to TM03 on the moves list in-battle. If everything is set up right, the screen will be corrupted by just the right amount of characters as in the video, with the last character being controlled by the Rival's name item in the expanded inventory.
2. Close the menu, open the items menu, use -g m
3. Press A on an unterminated name glitch item (e.g. 0x80), and back out
4. Use a Master Ball to catch your modified Pokémon, which will be based on the last character top-left to bottom-right you manipulated on the screen.
Perhaps you can write D069 to 00 with a more complex variation of this glitch (perhaps get a Glitch City with the Pokédex glitch item in battle and find a way of writing 00?), but unfortunately you can't use 00 directly from the Rival's name; they terminate the name as control characters.