A Bad Egg, named Bad EGG before Generation IV, is an Egg that one can obtain in all Generation III and on Pokémon games. Though the term is often also applied to glitched Eggs in general, it is only used in-game to refer to noticeably-corrupt Eggs, which result from the use of cheat devices such as Action Replay, or Poké-GTS.
Bad Eggs will hatch into another Bad Egg continuously. Bad Eggs will hatch every time the player moves 1 step; while in boxes Bad Eggs can duplicate. If one checks the summary it will say that it is obtained on 0/0/2000 at Mystery Zone.
Appearances[]
Generation II[]
It is possible to, through the use of a cheat device, catch an Egg in the wild or turn a Pokémon the player character already owns into an Egg. Such Eggs don't have any data specifying what they are supposed to hatch into, so the Egg simply hatches into more Eggs.
Sometimes, it is impossible to battle with a Bad EGG as its back sprite is undefined.
In these games, Bad EGG is called simply EGG.
Generation III[]
The Generation III games are the only games to actually make use of the term "Bad EGG". The string is used to identify Eggs that appear to have been corrupted. The Trainer Memo section of such Eggs' summaries invariably states that they are "A peculiar Egg obtained in a trade." Such Eggs do not actually hatch unless prompted by a cheat device.
The Elite Four in Generation III all have at least one Bad Egg in their party, when a cheat is utilized to capture their Pokémon.
Generation IV[]
In Generation IV, Bad Eggs are sometimes found by using a cheat to capture the opponent's Pokémon. Bad Eggs can also occur when one uses a cheat device to catch Pokémon in the wild that are not found in the game, like Regice in Pokémon Pearl, or Mesprit in Pokémon SoulSilver. A normal Pokémon in the PC becomes identified as 'Bad Egg'.
Generation V[]
In Generation V, many glitches have been fixed that involves a Bad Egg such as that the game no longer freezes or corrupts. However, the Bad Egg cannot be removed if a cheating device is not used. The Egg also cannot be used in a battle or be released. It acts like a normal Egg that never hatches. If one manages to get one that hatches, the Bad Egg acts like an ordinary Egg and freezes the game, a bug still remained unfixed.
You can encounter a Bad Egg in a wild battle if you modify your dex entries to make the numbers bigger than 649, though this Bad Egg will immediately flee. Even if you manage to capture it, it will have no dex entry and its info will be instantly erased.
Generation VI[]
There are reports of Bad Eggs appearing in Gen VI games.
Generation VII[]
There are reports of Bad Eggs appearing in Gen VII games.
Despite breeding and Eggs not being available in Let's Go Pikachu and Eevee, there is still a 2D and 3D sprite for an Egg in the files of the game and can be obtained by hacking. It acts similar to the Bad Egg. However, when used in battle, it will immediately faint. If your entire party is Bad Eggs, you will automatically lose. Healing the Bad Eggs at a PokéCenter crashes the game.