Old man glitch
From Bulbapedia, the community-driven Pokémon encyclopedia.
The Rare Candy Cheat is probably one of the most infamous glitches in the Pokémon games. It gives the trainer unlimited Rare Candies (or whatever item is in the sixth slot of your bag).
It is a side effect of the Missingno. bug, where the sixth item on your bag, not necessarily a Rare Candy, gets 127 copies of itself added. By using all of these but one and repeating the bug, the player can have an infinite amount of that item.
