The item duplication glitch in Pokémon Red (MissingNo. +128)

Meeting MissingNo. or 'M in Pokémon Red adds 128 to the quantity of the sixth item in your bag. Put the item you want (Rare Candy, Master Ball, Nugget) in slot six first, then trigger a MissingNo. encounter.

Why it works

The Pokédex keeps a "seen" flag for each species. MissingNo. and 'M have species number 0, whose flag sits just outside the Pokédex data: on the high bit of the sixth bag item's quantity. Seeing one sets that bit, adding 128. Quantities above 99 show as glitchy characters.

Tips

• Rare Candy is the classic choice: 128 of them max out several Pokémon.
• The bonus only applies once per slot while the flag is already set, so swap a new item into slot six before each encounter.
• Don't toss items with glitched quantities.