Siren (The Curse of the Black Spot)

The Siren was a virtual doctor, who took pirates from The Fancy in the 17th Century

Biology
The Siren took human form when she cared for humans. She could fly, and her singing acted like anesthetic. She could use it to lure individuals to her, although it only affect those from whom she had taken a tissue sample. On touching her, the humans would be teleported to a sick bay. Her screams were capable of knocking people around, as she did to Amy.

While in human form, when calm, she took the form of a beautiful woman with a cyan aura. When interfered with, however, she would become red and angry.

She refused to let anyone else help her patients, unless they were connected in some way, such as marriage. She then required them to place their hand in a glowing ring, for confirmation that they were taking over in caring. (DW: The Curse of the Black Spot)

Technology
The Siren could use anything that had a reflective surface as a portal to pass from one universe to the next. She could also use fire from her hands to sterilise things such as tissues. (DW: The Curse of the Black Spot)

History
The Siren worked on a space ship that landed on The Fancy. The crew where all wiped out by a illness leaving her with no patients on the ship. With nothing to do, she became aware of The Fancy's presence, and sensed any crew members who were wounded in the slightest way (for example, a small cut). She then took tissue samples of the wounded sailors, leaving a black spot so she could then return and take the sailor to the sick bay to care for them. During a storm, she took the Captain's son, Toby.

When Rory was knocked off the ship and began to drown, the Doctor exposed a reflective surface (as they had previously covered them up to prevent her from taking any more men) so the she could save him. The Doctor, Amy and Captain Avery all allowed themselves to be taken by the Siren to see where they were taken. When they found Rory and the crew, Amy showed the Siren her wedding ring, and the Siren gave her consent to care for Rory. Captain Avery knew that his son couldn't be saved, so took over the space ship with his crew, allowing the Siren to care for them. (DW: The Curse of the Black Spot).