One glitch I came upon was in gen 2 when I had tried to clone one of my pokémon. I ended up creating a chimaera between my Arcanine and my Golduck. Sometimes it would appear as a water type Arcanine with Golduck's moves, and sometimes as a fire type Golduck with Arcanine's moves. So I suppose in a way, back in the day I had accidentally created the mythical water type Arcanine that everybody now seems to want as a regional form! I've had a water type Arcanine before regional forms were cool!