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.
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.
