Mi'en Kalarash

The Mi'en Kalarash or "blue fire", was an ancient myth from Gallifrey, said to inhabit "the wasteland between realities". It fed on nightmares. The creature itself was composed of a series of minute slivers in incremental time, a "time magnet". Its outward appearance was a tall, thin humanoid figure with dark leathery skin, a bestial face, all swathed in blue fire. (BFA: House of Blue Fire)

The Mi'en Kalarash was one of the Elder Gods. (BFA: Black and White)