It’s the Time Lord way of cheating death, but though it means he continues living, it’s not without its drawbacks, nor is it painless. It’s like an all-consuming fire, searing through every cell of his body, burning away his old self, creating him anew.
Golden flames race along his nerves, shimmer across his skin, forming his body into a new shape, no longer suffering the damage that was killing his old one. When it fades away, he’s unrecognisable, even to himself, and must embark on a voyage of rediscovery to learn who he’s become.
He doesn’t always like the answer.