Bad Egg
Bad eggs first appeared in the advanced series of Pokémon games. It is the typical result when data for a Pokémon is corrupted, either by the user changing it using a cheating device, normal save file corruption, or a transfer error. A bad egg is not actually a Pokémon egg, and very well may have never been, but because of the way the 16-bit checksum value works in the Pokémon's data structure, this default message might appear.
The bad egg will have a type ???, may sometimes be holding an item, and depending upon the way the data is manipulated, it may be reported to have the PokéRus and/or the small black dot associated with it. The owner's ID and OT values are both set to "?????," like those on a normal egg are.
The gameshark code for quick level up in the daycare will result in an invisible bad egg. This bad egg can be switched with the last Pokémon in the party via PC and can be used in battle. Its battle image is a black egg, while its summary image is a black circle with a white ? in it. Using this in battle with cause instant white out. The egg can be deleted if it is picked up while holding another Pokémon in the box and set back down. This egg cab also be encountered by using the "catch pokemon easily code" and using a pokeball on a trainer's pokemon. I'm not sure what hatches from it though :( Template:Gamestub
