Have an empty box 1 that has never had 20 Pokémon. This is important. On real hardware DA94, the end marker for a box will always be FF in box 1 if you've had 20 Pokémon, but it will be 00 if you've never had more than 19 Pokémon there.
If the box is not empty but you have had Pokémon in it before the glitch may work differently, with the player possibly having to deposit more Pokémon or something than the maximum number of Pokémon they had.
You cannot use boxes 2-10; and if these boxes did work it would be an emulation error (due to these boxes by default being filled with FF bytes).
Another thing you need is a box other than box 1 with e.g. 5 or more Pokémon in it for you to withdraw to get a full party.
1) Have six Pokémon in the party, including a Pokémon with a catch rate of 255 as the first Pokémon and the remaining HP of your choice, four other Pokémon and a Q, index number: FF which can be obtained by evolving 4 4Hy, Ditto glitch special: 192 at level 6.
2) Deposit the Pokémon in box 1 in order, so the catch rate 255, chosen remaining HP Pokémon comes first, except when you get to the fifth one, where you deposit Q last. Remember you can't deposit your last Pokémon, which is why we need 6.
Example box order:
3) Change to another box and get a full party. Then change back to box 1.
4) Capture a Pokémon (may need catch rate of 255) and this will send it to the first position of box 1.
Example box order:
5) Change to the other box, and deposit all Pokémon but the first. Then change back to box 1.
6) Withdraw your Q. You'll notice your first Pokémon's level change if done correctly, but there's still room for mistakes.
7) Do these withdrawals in order:
Withdraw Poké #1
Withdraw what is now Poké #4 example: Pikachu
Withdraw what is now Poké #3 example: Sandshrew
Withdraw Poké #1 example: Caterpie
Deposit Q, heal your Pokémon, then go to the Daycare, deposit and receive your affected Pokémon to get the converted Pokémon.
For example, if the Pokémon with the relevant remaining HP was 253 or FD, you would get the hex:FD Pokémon.