The Mystery Egg (Japanese: ふしぎなタマゴ Mystery Egg) is a Key Item introduced in Generation II. It is an unusual egg found by the Day-Care Couple and given to Mr. Pokémon.
Mr. Pokémon asks the player to bring the Mystery Egg to Professor Elm for study, due to his expertise on Pokémon Evolution. After the player defeats Falkner and obtains the Feather Badge, Elm's aide will return the egg to the player, revealing that it is in fact a Pokémon Egg. The Egg, if the player chooses to keep it in their party, will eventually hatch into a Togepi. If the player shows the hatched Togepi to Professor Elm, he will give the player an Everstone.