A Geodude affected by the glitch
Infinitely long enemy Pokémon name is a glitch in Pokémon Yellow, and a sub-glitch of "wild appeared!".
This glitch involves the unterminated name of the enemy Pokémon and the 0x59 character following (responsible here for printing the enemy Pokémon's name), responsible for an infinite loop because the name continues to reference itself.
If you have ~241 Pokémon+ the enemy Pokémon's name gets corrupted with values $32-$34.
Now, if the Pokémon's name gets corrupted to be greater than 10 characters long (251 Pokémon in Yellow, 252 Pokémon in Red/Blue) then there will be no 50h terminator in the name; so the game will read unrelated data past CFE4/CFE3 as text character data.
But since a few addresses up to 'enemy status': CFE8 (the equivalent of this is CFE9 in Red/Blue) are likely to be 0 ('terminating' the name) this doesn't become a problem unless you have exactly 0 (256) Pokémon in Yellow to corrupt up to CFE8 with the $32-$34 values.
You can enter a battle with 0 Pokémon without cheating by viewing a Pokémon with Super Glitch as its first move when you are on the deposit menu in a PC. Incidentally, this may cause a walking lag effect.
If the game grabs a hex:59 character from the data past a Pokémon's name, such as the Earthquake in a wild Geodude's moveset, you can cause the game to try and print an infinitely long name.
When the infinite name effect happens, it is because hex:59 is a control character that can print "Enemy (Enemy's name)". Since the enemy's name has a hex:59 in it itself, it becomes an infinitely long name like "(spaces)9(right arrow)Enemy" (repeat). This is similar to what happens with hex:F0's conditionally infinite name in Spanish Red/Blue because that glitch Pokémon has a hex:59 character in it.
- Dragon59095: Research on how a Pokémon's nickname can be changed with wild appeared!
- ChickasaurusGL: Further research, video, article description