Shoal of the Winter Harmony
The Shoal of the Winter Harmony were a race of humanoids whose heads were split in two by a diagonal slash. They could separate the halves of their heads at will and were able to hide objects inside. Their race were conquered by King Hydroflax.
Their usual appearance was a living brain with eyes. They were able to removing a living being's brain and transplant themselves in the vessel, thus allowing them to pass for humanoid.
Appearances
The Husbands of River Song (TV)
The Return of Doctor Mysterio (TV)