Sketch glitch (Generation II)

Something which I meant to upload footage of a long time ago, but never got around to doing so (not to be confused with the popular Final Fantasy series sketch glitch). This is an old glitch found in the early days of Generation II. If a Pokémon which used Transform successfully performs Sketch, then the move Transform (or Metronome if Transform was used via Metronome) will be replaced with the Sketched move at the end of the battle in a similar way to the Mimic/Transform/Rage glitch from Generation IV. The moves can then be passed on through breeding with Pokémon in the same egg group to obtain more Pokémon with illegitimate movesets (without using glitches such as the Pokémon merge glitch/Q glitch) or cloning glitches/Celebi glitch.

Since wild Smeargle have no other move than Sketch, the player needs to use Mystery Gift to fight another player with a Smeargle knowing Sketch and at least one other Sketchable move in the Trainer House. (or perhaps via Link Battle, though I haven't tested that yet). More details can be found on the Bulbapedia article which I started in February last year.