Elysian field
An elysian field was a method, using cyrogenetic extraction, that allowed a Time Lord to completely break down their body into it's components, i.e. atoms and molecules, and rebuild themselves, editing their personality. It could spark regeneration, even at the end of a regeneration cycle, and thus was banned by the Time Lords.
When her previous incarnation shot her, wounding her beyond the ability to regenerate, (TV: The Doctor Falls) Missy used an elysian field to survive and regenerate, removing all her "snide" evil and leaving only the kindness, in a final act of bad against the Time Lords and in the hopes of impressing the Doctor. This new incarnation was entirely good, remembering some of her past actions but not all, and naming herself the Lumiat. (AUDIO: The Lumiat)
