The Raak

The Raak was a sea creature that lived on Thoros-Beta. It had a huge domed head with a basilisk eye, clawed and suckered hands and powerful tentacles. (PROSE: Mindwarp)

Crozier experimented on it and succeeded it making it almost docile, placed in a cave to protect the auxiliary tidal regulator. Representing his greatest success thus far, both he and Matrona Kani were upset and angry when the Sixth Doctor and Peri Brown accidentally killed it using a phaser. Much to Crozier's chagrin, it had regressed into savagery and attacked the pair. (TV: Mindwarp)