Gastrodon

Diamond: It has a pliable body without any bones. If any part of its body is torn off, it grows right back.

Pearl +2: It apparently had a huge shell for protection in ancient times. It lives in shallow tidal pools.

Platinum +4: Long ago, its entire back was shielded with a sturdy shell. There are traces of it left in its cells.

HeartGold +3: When its natural enemy attacks, it oozes purple fluid and escapes.

Sun: 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.

Moon: Plankton, invisible to the naked eye, is its main food source. It comes onto the land periodically, but the reason for this is not known.

Ultra Sun: Long ago, it had a shell on its back. There’s now a vestigial plate on its back that’s hard but thin.

Ultra Moon: Their shape and color change, depending on their environment and diet. There are many of them at beaches where the waves are calm.

Sword: Its search for food sometimes leads it onto land, where it leaves behind a sticky trail of slime as it passes through.

Shield: The softness of its body helps disperse the force of impacts, so although its body is uncommonly squishy, it’s also surprisingly resilient.

Legends: Arceus: Eats beach sand for nourishment. Should one Gastrodon encounter another of a different color, a fierce battle will inevitably ensue.