Medusa (species)

The Medusa was a predator alien species. The Fourth Doctor described them as vile. A Medusa was able to quantum-lock a person, making them petrified.

People who had been petrified were, however, still alive, frozen in time, preserved, so the Medusa could feed on their life energy for years, centuries, even. When the Medusa was done feeding, the petrified person turned to dust. The Medusa were trapped on Earth. (COMIC: Gaze of the Medusa)

Biology
The Medusa looked like a humanoid-snake hybrid. She had dark, green scaly skin, black hair, sharp claws, a large jaw and a massive tail instead of a pair of legs.

Powers and abilities
The Medusa was capable of quantum locking. However, unlike the Weeping Angels who used this as a defense mechanism to petrify themselves, the Medusa quantum locked her prey. This was accomplished by emitting a beam of blue light from her eyes. Anything caught in its path was turned to stone. In this state, they were immune to the effects of time and were preserved indefinitely but were also helpless. Victims could sometimes only be partially petrified, in which case their movement was hindered and they would slowly turn to stone. The process was described as painful to humans.

The Medusa fed off the life energy of other sentient species. The longer they lived, the more energy she could feed off. When observing the Fourth Doctor, she recognized him as a Time Lord and stated that he alone could feed her for centuries. Once she had fed off all the life energy of a petrified victim, the subject died and crumbled into dust.

The Medusa also displayed potent telepathic powers. She could easily mentally control humans and Scrylops into doing her bidding but proved unable to control the Doctor. She also possessed consciousness transferral, the ability to transfer her living mind into another body. When doing so, the host's mind was obliterated, killing them. The body was then quantum locked before the Medusa emerged after having biologically modified her host body into a new form similar to her original body.