This glitch may not work on certain emulators due to its abuse of specific CPU timing.
Although this location within the opponent Trainer's Pokémon data is tricky to manipulate, it can be made to run the Hall of Fame script. However, in order to run the Hall of Fame script a specific Trainer ID, player name, stored Pokémon data and some luck is involved. This includes having a 'good' current play time specific up to how many frames have passed before the next second.
First name your player mMna.♀tF (the name is important) and manipulate the Trainer ID 61896 (F1C8), also important. Choose Charmander or Bulbasaur as the starter. It will get the ID 61896 which is necessary for the run.
Note: A different player name and Trainer ID have been used for TAS purposes, but these haven't been examined for non-TAS use yet.
Now continue the game as normal until you get to Viridian City, in which you should find a Spearow on Route 22 and name it "AAA". Then deposit your starter into the PC and use the 'death-warp' technique to blackout on the last Bug Catcher.
This means getting an encounter in the grass in the Bug Catcher's vision and fainting. This causes you to black out but sets up an instant encounter when you return. If using luck manipulation you can encounter a Pikachu to faint Spearow, otherwise poison Spearow beforehand.
Now, don't open the start menu or open any text boxes (or the glitch won't work properly) and return to Viridian Forest. You will re-fight the Bug Catcher. Win or lose against him, then you will immediately battle him again (again you can win or lose this fight). This activates glitch meta-map script 06, which causes lag when you walk and can interrupt A button presses.
Next save the game south outside of Viridian Forest to be safe, as your play time (including frames) can affect the upcoming Hall of Fame warp. Proceed to the first Bug Catcher you can fight and mash A until you get his encounter text to appear.
Win the fight and if lucky, you will enter the Hall of Fame.
If you want to do this with no luck manipulation, obtain the ID 61896 by swapping a quantity of 241 into item 30 and a HM05 into item 31 (see expanded items pack), then obtain a Charmander at Level 6 from the Trainer escape glitch and trade it over to the new game to deposit it into the PC.
You will still have to be lucky to encounter Spearow, get the death-warp and get Hall of Fame to work however.
For instant encounters from Trainer battles the game uses something called 'meta-map scripts'. These are scripts for a number of maps to perform a task (such as to encounter the Trainer, to stop the player from leaving Pallet Town into Route 1 and so on).
Due to a glitch beating the Trainer two times sets the meta-map script to glitch value 06. This causes walking lag. Proceeding to beat the other Trainer will execute F8FF in Echo RAM (in the middle of enemy Pokémon 3's data), in which copies of the player's name are executed as code. The code falls through to play time (in which the values including frames need to be 'safe'), and then to the stored Pokémon's data.
Here if we have exactly 1 specific Pokémon with the right ID you can proceed to execute the Hall of Fame script.
TheZZAZZGlitch also did further research into this. Apparently the execution of F8FF is due to an invalid predefined command function 0xF4. Apparently the code is supposed to execute F808 but ends up executing F8FF due to a VRAM inaccessibility related detail.
This glitch may not work on VisualBoyAdvance, Pokémon Stadium 2 or possibly Nintendo 3DS Virtual Console.