Gastrodon — every printing, every price, every gap.

It has a pliable body without any bones. If any part of its body is torn off, it grows right back. It apparently had a huge shell for protection in ancient times. It lives in shallow tidal pools. Long ago, its entire back was shielded with a sturdy shell. There are traces of it left in its cells. When its natural enemy attacks, it oozes purple fluid and escapes. It has strong regenerative capabilities. Even if parts of it are bitten off by fish Pokémon, it will return to normal within a few hours.