The Moon Ball is a special Pokeball that can only catch Pokemon who evolve from a MoonStone. However, it can only catch 4 of those 6 pokemon, which are: Nidorino, Nidoran, Clefairy, and Jigglypuff.

The other two it can not catch are: Munna and Skitty. The games that feature Skitty have no available Moon Ball and Munna was not introduced until Generation 5, where the Moon Ball was not available.