Yayani was a Time Lord.
She suffered from Abridgement Syndrome which meant that she was not able to regenerate at all. She came from the House of Stillhaven and when Rassilon had all the members of the house taken away and experimented on after having their memories wiped. She was only able to remember due to her finding a recall cube that her brother left behind. Following this, she attempted to kill Rassilon but was stopped and given a choice: be executed or work for the General.
Following a mission alongside Missy, where they were to stop time experiments conducted in the 28th century, which would reveal that Gallifrey hadn't been destroyed, she was killed by Missy using her TCE. (PROSE: Lords and Masters)
Appearance
Yayani was dark skinned, with almost fully black eyes and short blonde hair. She was also taller than Missy.