The true form of a Carrionite resembled a giant skeletal raven or crow. They were able to assume a more humanoid form but this used a lot of energy, and so they usually had wrinkled skin, large, clawed hands, and sharp canine teeth. The Carrionite Lilith could assume the form of a beautiful young woman, a trick she used to ensnare male victims. (TV: The Shakespeare Code)
Carrionite technology was described as witchcraft. It was actually a word-based science, as opposed to the mathematics of most species, and may be similar to quantum mnemonics. It relied on the right words and the right places, such as the Carrionite's use of the Globe Theatre's structure. They also placed great importance on knowing the name of an individual to give them control.
With this linguistic technology for a basis, the Carrionites had a wide variety of abilities. They used both poppets and puppets as DNA replication modules to cause damage from afar or control a person's actions. This required a tissue sample, such as a hair, to work. They could also fly, dematerialise and rematerialise at will, communicate with other Carrionites from a distance and had the ability to discover a person's name and use it against them, even sensing if those they named were out of their time, like Martha Jones. The Doctor, however, was mostly immune to such, though Lilith could detect a name that strongly connected to him; Rose. (TV: The Shakespeare Code)
At "the dawn of the Universe", the Carrionites evolved in their 14-planet star system and developed their word-based science. (TV: The Shakespeare Code) Eventually, the Carrionites got into a war with the Hervoken. This war threatened the structure of the universe, so the Eternals stepped in and banished both races to the Deep Darkness. (PROSE: Forever Autumn)
Several million years later, in the late 16th century, a group of three Carrionites — Bloodtide, Doomfinger and Lilith — escaped using words of power from the plays of William Shakespeare, partly the result of the writer's grief at the death of his son. They influenced the design of the 14-sided Globe Theatre, based on the planets of their star system, and, in 1599, planned to use his new play, Love's Labour's Won, to free the rest of their race from the Darkness and take over Earth, removing humanity from it as a pestilence, to establish the "Millennium of Blood".
The last few lines of the play were written by Shakespeare in a trance as a spell said by one of the cast to open a portal from the Deep Darkness to this universe. However, the portal was closed and the race of witches and all copies of Love's Labours Won vanished into the Darkness, thanks to the help of the Tenth Doctor. He told Shakespeare that he was "the wordsmith" and could create the new words of power to send them back into the Darkness, and Martha Jones, who provided the last word — "Expelliarmus" — from the Harry Potter series of novels. The escaped Carrionites were trapped within a crystal ball. (TV: The Shakespeare Code) The Doctor kept the crystal ball in his TARDIS. (TV: The Unicorn and the Wasp, PROSE: The Taking of Chelsea 426)
The Sixth Doctor encountered a set of Carrionites in the 1980s. They inhabited some of the locals in Birmingham. They used the Paradox of the fact that the Tenth Doctor defeated them in their past and the walls of the local council had been built from the remains of the Globe. (AUDIO: The Carrionite Curse)