The standard Poké Ball is your basic catching tool. Great Balls offer a higher catch rate, and Ultra Balls are even more effective. Master Balls guarantee a catch but are extremely rare (usually only one per game). Safari Balls are used exclusively in the Safari Zone. Net Balls are more effective on Water and Bug-type Pokémon, while Dive Balls are better for Pokémon encountered underwater (though not applicable in FRLG). Timer Balls become more effective as the battle lengthens.
