The Lavender Purpureus Shell is a unique double-spiral shell, the inside of which is covered with nacre. When pressed against the chest, the mermaid shell instantaneously billows out in a cloud and transforms the owner's lower body into that of an octopus.

To transform back, the octopus part of the owner must be soaked in blood. While the blood may be watered down, the entire tail must be submerged in a liquid that is red with blood, requiring at least three points of blood are spent, though non-human blood can be used. Once soaked, the transformation is reverted immediately, and the shell materializes again. Alternatively, the transformation will also revert if the wearer of the tail does not touch any liquids for 48 hours.

The octopus tentacles start out black at the hips, but range through dark blue into a deep red at the tips.

Injuries sustained when transformed remain on the lower body when the transformation is reverted, and injuries sustained before transforming remain when transformed. If other clothing, jewellery, equipment and so on is worn on the lower body, the transformation fails, though very close fitting items or garments such as underwear can merge into the transformation. In that case, they will not be available until the transformation is reverted.

While transformed, the shell grants the owner of the following abilities (and drawbacks):

Octopus tentacles The shell grants the lower body of an octopus or squid. While the wearer has control over these tentacles and can grab objects with them, they cannot be used to operate machines, tools, firearms, etc., other then pulling, for example, large levers. The octopus tentacles do lend themselves to swimming, and as such your swim speed is calculated as 10 + Athletics + Strength + 2 × Acrobatics, not counting any other bonuses.

Sea Adaptation While transformed, you can breathe while under water, and are protected from the cold as if you were wearing dry, warm clothing suitable for cold weather, even if mostly exposed.

Land movement On land the wearer can still move around, but is limited in their overland speed moving only four squares using the Move action and cannot use the Retreat or Reposition actions (see the rules for Combat for details).

Sea-witch affinity While transformed, the wearer is strongly associated with sea witches. This influences their ability to use curse and water-related rituals. If the witch botches a roll to activate a curse or water-related ritual, they may reroll the activation roll. The new result will be used, even if it is a second botch.