Pokémon merge glitch

The Pokémon merge glitch, commonly known as the Q ◣ glitch, is a glitch in the Generation I and core series games. It is enabled by the glitch Pokémon with index number 0xFF (Q ◣, 'M (FF), and ????? (FF)). It involves depositing that glitch Pokémon and other Pokémon into the Pokémon Storage System in a certain order, which then causes the Pokémon's moves and stats to be transferred between each other, creating an unstable hybrid Pokémon.

Performing the glitch
First, the player must have a Q ◣, 'M (FF) or ????? (FF), at least one Pokémon above it and two Pokémon below it, all in the party. The Pokémon below the Q ◣, 'M (FF) or ????? (FF) will be the 'donor' to the Pokémon below it; that Pokémon will then be the donor to the Pokémon below it, etc. The Q ◣, 'M (FF) or ????? (FF) will appear in the top slot where the deposited Pokémon was, but also stay in its original spot and be the donor to the Pokémon directly below it.

Each Pokémon is now an 'unstable hybrid' of it and the Pokémon that was below it. An unstable hybrid cannot be traded from a Generation I game to Pokémon Gold, Silver, or Crystal. An unstable hybrid displays the sprite, mini-sprite and type of the 'donor' Pokémon, and evolves in the same way as it. It has the species name (shown on the second page of the summary screen), learnset, TM/HM compatibility and effective type combination of the donor Pokémon. In Generation I, an unstable hybrid Pokémon has the color palette of the recipient; in Generation II, it has the back sprite and palette of the recipient. Unstable hybrids created with the Pokémon merge glitch have the recipient's nickname.

Stabilizing
To stabilize an unstable hybrid Pokémon, a Pokémon can be evolved (in the way the donor would), traded to Pokémon Stadium 2 (this makes both species bytes match the recipient), or deposited and withdrawn from Pokémon Day Care (this makes both species bytes match the recipient). Once stabilized, the Pokémon can be traded to the Generation II games.