Sun-Stealer
From Tardis Wiki, the free Doctor Who reference
The Sun-Stealer was an unlimited power source located on Tavos. Missy had plans to steal it, but knew that the Tavosian Union would die trying to protect it, but she was prepared to commit genocide anyway before the Time Lords forced her to go on a mission to the Kyme Institute where she found a better power source for her TARDIS. (PROSE: Lords and Masters)
