In Pokémon Crystal, I encountered a shiny Grimer. I didn't have any Pokemon on my team to weaken it, so I threw an Ultra Ball, but it popped out. It fled. Apparently, Grimer are some of the few Pokemon coded with a high rate of fleeing in a generation 2 game. :( I did end up hunting for a shiny Grimer in Pokemon Violet recently to avenge it.
In Pokemon Violet, I encountered a shiny Hoppip. I didn't check its moves before trying to lower its HP. It used Memento and fainted itself.
Those are the only ones I can remember at this time.