Why do Pokemon turn into bad egg?

Answer 1

They don't usually turn into one... It's usually because A GameShark/Action Replay/CodeBreaker code is conflicting or incorrect, usually when getting a hackemon. (Hacked Pokemon) Can also be received when using "Catch Trainer Pokemon" AR code, but it is rare. Occasionally it will say "You caught Bad Egg" but in the box or party it will usually be the one you tried to catch... (Also can be encountered in wild using "Encounter Calculator" AR code and typing in 495, it caused the game to crash when I did it though)

[The Gray Wolf]

Pokemon do turn into bad eggs actually this happens when a Pokemon is kept in the PC with the bad eggs, the next time the Pokemon is picked up it's Sprite looks like a bad egg and you when veiw it's summary and it transforms into a bad egg this is what some bad eggs do these bad eggs are called Mutator eggs these are the secound most dangerous type of bad eggs being behind corrupter eggs there are 10 types of bad eggs that Nintendo made mutator eggs just do that's all part of the torture Nintendo do to cheaters.