A magical sea shell
To drain the life force of beings and even their immortality
The Sea Hag tried to use an Auger Shell to drain the immortality of the mermaid Mylie, so that she could give her immortality to the undead demon Necron. However, she needed to persuade the mermaid to willingly give up her immortality or it would not work. Phoebe Halliwell later used the Auger Shell to kill the Sea Hag, reducing her to dust. Necron used it on Phoebe after she became a mermaid, but Paige orbed it onto Necron to distract him. However, as an undead being, he was not affected.