Mark 212

The Mark 212 ("two twelve"), nicknamed "Mark" by Detective Joe Lynwood, was a new TARDIS type developed during the Last Great Time War and piloted by the Master. Upon gaining sentience, Mark realised the Master had made it do horrible things, and so fled, searching for a new pilot. Though it found many, Missy eventually used Lynwood to take control of the TARDIS and continue causing mayhem throughout the universe. However, an older Lynwood travelled back in time and revealed to Mark that Missy was in fact the Master. While Joe escaped, Mark began to self-destruct, taking Missy with him, but Missy found the "factory reset" just in time to save herself. (AUDIO: The Broken Clock)

Later while finalising the Master TARDIS, Missy threw Mark into the Eye of Harmony as a way of cannibalising her TARDIS. (AUDIO: The Belly of the Beast)