Neptune's Shell

 is an equipable item that transforms the wearer into merfolk when they enter water. In this state the player has the ability to breathe underwater, swim as if they had flippers, and isn't slowed down like normal. The effect instantly wears off as they leave the body of water. It can also be upgraded to a Moon shell at the Tinkerer's Workshop with a Moon Charm.



Bugs

 * If the player goes directly from lava to water, they will not transform until they leave and re-enter the water.
 * Wearing the shell will make wings fail to work when jumping out of water one block deep or more (enough to cause the transformation), requiring the player lands/grapples/grabs on a non-submerged surface to be able to use the wings again.