Ditto Whoring

A tactic in any handheld-console pokemon game where, immediately after the player obtains the transforming pokemon, Ditto, he or she places it in the day care and never takes it out.

In the day care, another pokemon is placed with the ditto so that it will produce an egg, either to obtain a pokemon only obtainable by egg or to simply reproduce it to trade it off in the Global Trade Center (GTC) for a rarer pokemon.