Capricorn Helmet

The set covers a head, a body and a leg slot, but the leg slot comes in two versions: hooves or a tail. They are two separate items rather than one item with a switch, which is why the set lists four entries while only ever filling three social slots at once. Capricorn is the sea goat, so the hooves cover the goat half and the tail covers the fish half, and you decide which half you want to be. All of it is appearance only.

The swap happens while the item is sitting in your inventory rather than equipped. Press your open or activate key on it and it turns into the other version where it stands, favorite flag intact, so you are not digging through your bags afterward looking for a fresh item that appeared somewhere else. Journey Mode is where the split matters: the hooves and the tail are researched separately, so unlocking one does nothing for the other and you need copies of both.

It is one of six outfits that came out of the community vanity contest for the 1.4 update, from a concept by R-MK. The tail's tooltip is a nod to the small group of items that let you swim properly instead of flailing at the surface.