As guessed the latest Season Eight ally to join Doctor Who Legacy is Saibra the shape-shifting member of #teamdead from Time Heist. She is a 100% drop from the Time Heist special level which just has The Tiller as its challenge in a single level.

Her colour is blue (not sure about her secondary colour) and her power is the ability to massively increase the damage of a random colour. I like the uncertainty of this and it is in line with the Orson Pink power of random gem colour change.