Pokémon Gold Version, Silver Version, and Crystal Version - Walkthrough - Pokémon Daycare
This information might be useful when playing Pokémon HeartGold Version and Pokémon SoulSilver Version, too.
On Route 34, below Goldenrod City, there is an old man and woman who will each care for one of your Pokémon for you. Talk to the man to give him a Pokémon to care for; the old woman will do the same. When you ask for the Pokémon back, you’ll be charged 100, plus 100 for every level the Pokémon gains.
Because you’ll be able to care for two Pokémon at once, and because the Pokémon come in different genders, you’ll be able to "breed" Pokémon to get new varieties. To breed Pokémon you must give the old man a Male Pokémon and give the old woman a Female Pokémon (or vice versa) that have the same little icon or sprite. Then, exit the center. Some time later, return to the day-care. Come back when you see the man standing outside with your two Pokémon. Talk to him and answer yes, and he will give you an Egg. If the Pokémon you bred are of different species, the Egg will be a Pokémon with the same species as the female, and will know an attack that the male had.
Special Pre-Evolution Pokémon
Odd Egg
In Pokémon Crystal Version, talk to the old man and you’ll get an Odd Egg. Walk around with it, and it’ll hatch into Igglybuff, Pichu, Cleffa, Magby, Elekid, or Smoochum. It’ll either be shiny or have weak stats, and it’ll know the attack Dizzy Punch.