Summary of "How To Duplicate Items (Mail Glitch Guide) Pokemon Fire Red & Leaf Green"

Duplication (mail) glitch in Pokémon FireRed / LeafGreen

What the glitch does

Lets you duplicate virtually any held item (Nuggets, Rare Candies, Master Balls, TMs, etc.).
Once set up, you can repeatedly duplicate items by using mail swaps — you don’t need to redo the full double-battle setup each time.
Works on current Switch releases (per the referenced video). The older “Nugget exploit” (farming a Rocket trainer on Route 24) is also mentioned but is less flexible and has language/version limitations.

Requirements

Two traded Pokémon:
- Farfetch’d (acquired by trading another Pokémon).
- Mr. Mime (acquired by trading Abra in the video).
Moves:
- Farfetch’d must know Knock Off (learned around level ~21 in the video).
- Mr. Mime must know Recycle (learned around level ~33 in the video).
Two items:
- A recovering berry (an Oran/Orange-style berry) that can be eaten in battle.
- A mail envelope from the department store (Celadon/Saladon City in the video).
A nearby double battle (the video uses the double battle just west of Celadon/Saladon City; the Versus Seeker can be used to refight).

Step-by-step duplication setup (condensed)

Obtain and train:
- Get Farfetch’d via trade and raise it until it learns Knock Off.
- Get Mr. Mime via trade and raise it until it learns Recycle.
- Obtain a health-restoring berry and a mail envelope.
Prepare before the double battle:
- Have three Pokémon in your party: the donor Pokémon (any — the video uses Venusaur), Farfetch’d, and Mr. Mime.
- Give Mr. Mime the mail and name the mail something consistent (the video uses the name “Abra”).
- Make a save.
Execute the double battle trick:
- Cause the donor Pokémon to eat its berry (have it take damage so it uses the berry).
- Use Farfetch’d to select Knock Off and arrange to have the donor swapped out for Mr. Mime so Knock Off hits Mr. Mime and knocks the mail off.
- While Mr. Mime is on the field, use Recycle — the game gets confused and recycles the donor’s berry instead of returning the mail.
- Finish the battle (winning or losing doesn’t matter). After the fight, Mr. Mime will no longer be holding the mail. If something goes wrong (a Pokémon dies or gets trapped), reload your save and retry.
Do the duplication at a Pokémon Center:
- Fill your team with six Pokémon.
- Give five Pokémon mail items all named identically to the original mail (the same name used earlier).
- Give the sixth Pokémon the item you want to duplicate (for example, a Nugget).
- Attempt to give that sixth Pokémon mail — when prompted to swap, accept. The mail naming screen will display question marks; skip it.
- The mail will convert into a copy of the held item in your bag while the Pokémon continues to hold the original item.
- Repeat: give mail to the same sixth Pokémon again to create additional copies. This can be repeated indefinitely.

Warning: If the double battle goes wrong (donor Pokémon faints or gets trapped), reload the save made before the double battle and try again.

Key tips, caveats, and notes

For unique TMs or one-of-a-kind items, keep at least one copy in your bag so you can duplicate it later.
The basic Nugget-exploit (losing to a Rocket trainer) is simpler but limited by language/version and missable conditions; the mail duplication glitch is more powerful and flexible.
The video demonstrates the glitch functioning on the Switch version.
If anything unexpected happens during the battle (e.g., permanent faint or status that prevents the setup), reload and retry from the pre-battle save.

Sources / people featured

The video narrator/creator (unnamed in the subtitles).
The trick is noted as being discovered/used by the speedrunning community (mentioned in the subtitles).
No other external creators or gamers are named in the subtitles.