|Buff tooltip||Can breathe and move easily underwater|
Neptune's Shell is a Hardmode accessory that aids underwater performance (and other liquids) by granting indefinite breathing time underwater, swimming via the ↷ Jump key, and eliminating the slow movement speed usually caused by water. Entering water with this accessory equipped transforms the player into Merfolk form. While in this form, the breath meter will not display (nor will it decrease), therefore effectively preventing drowning.
Neptune's Shell can be considered an upgrade from the Diving Gear in most respects, but lacks extra mobility on ice of the Arctic Diving Gear and the extra lighting underwater of the Jellyfish Necklace, though any light pet will compensate for this loss.
- Wearing the Fish Bowl will not activate the Merfolk buff.
- Swimming speed nears that of flying through air with Wings.
- Swimming in Honey activates all the perks of Merfolk but does not allow you to move at full speed.
- Swimming in Lava does not activate the Merfolk form.
- Landing in and "jumping" from water alone (by swimming up past the surface), without touching land, does not reset flight time for Wings or variants of Rocket Boots.
- The Merfolk buff overrides the Werewolf buff, replacing the graphics and canceling the bonuses granted by the Moon Charm during the night.
- The Merfolk form is affected by Dyes.
- Neptune's Shell can also be equipped as a vanity accessory, which causes the Merfolk form to appear regardless of whether the player is in water. This is merely the appearance of the Merfolk, the buff will not take effect while it is equipped as a vanity (caution should be taken when in water, as the player will need to watch their breath meter).
- Half of the ingredients can be obtained pre-Hardmode, so it pays to collect them as early as possible.
- The name of the item refers to Neptune, Roman god of the sea.