Abnormal Pokémon (Japanese: いじょうポケモン) is a blanket term for untradeable Pokémon in Generation II, not to be confused with glitch Pokémon.
It is an error trap used to prevent players from trading glitchy Pokémon, even if not much harm would be caused after trading them.
When the player attempts to trade an abnormal Pokémon, either between two Generation II games, or from Generation I to Generation II, they will get the message "Your friend's (Pokémon name) appears to be abnormal!" (Japanese: あいてがわが えらんだ(Pokémon name)に いじょうが あるようです!!, literally meaning: "The (Pokémon name) you chose from the other [Trainer] appears to be abnormal!!")
There is another message that says "Sorry, but your POKéMON appears to be abnormal. We can't accept it." The untranslated version was apparently used for when attempting to deposit an abnormal Pokémon up for trade using the Mobile System GB.
What defines an abnormal Pokémon
If a Pokémon meets the following conditions, it may be labelled as abnormal:
- If it is an unstable hybrid: The Pokémon must not be a hybrid (both species bytes must match), unless it's an Egg. It is possible to trade a Pokémon like this from Generation II into Generation I though.
- If it is over level 100: The Pokémon's level must not be over level 100.
- If its types are wrong: The Pokémon's types (stored in memory) must be correct, unless the Pokémon is a Magnemite or Magneton because they gained the Steel type in Generation II.
Notably missing are invalid Pokémon (though Generation I glitch Pokémon likely have types that do not match with their equivalent Generation II Pokémon), ????? (though the FE kind in Gold/Silver causes a glitch that prevents trading it) and Pokémon with impossible moves.
It is possible to trade a Cooltrainer move Ditto into Generation II to get the equivalent hex:00 glitch move there.