- You may be looking for the Master's TARDIS.
The Master TARDIS, as Missy called it, was as she described the "one TARDIS to control all others." (AUDIO: The Broken Clock) It was meant to find and control other TARDISes and bring them to her, but she found none. (AUDIO: The Lumiat)
The Master TARDIS was swallowed by a space creature, which caused it to grow to the size of a minor planet and turn to stone. Damaged, the TARDIS experienced dimensional leakage and released artron radiation. Using clone slaves, Missy dug through the creature to get to the TARDIS and eventually reached it.
Inside the TARDIS, Missy used a component taken from the Monk's TARDIS (AUDIO: The Broken Clock) and threw her own Time War-era Mark 212 TARDIS, (AUDIO: The Broken Clock) whom she trapped in a grandfather clock already inside the Master TARDIS, into the new "super duper" Eye of Harmony as a way of cannibalising her TARDIS. Finally, she used the star of the system containing the space creature to create a supernova to power her new ship. (AUDIO: The Belly of the Beast)