Retro-regeneration



Retro-regeneration was the process of regenerations being forced in reverse, causing the Time Lord in question to revert to previous incarnations, (COMIC: The Fountains of Forever) known only to be attempted by Time Lords of the First Rank (PROSE: State of Change) though it was not known to be permanent in any cases. (COMIC: Timeslip, COMIC: The Fountains of Forever)

The Fourth Doctor and his TARDIS were once infected by a space amoeba, which caused him to and revert to his third, second, and first incarnations as he rapidly slid back through all of his past selves. (COMIC: Timeslip) The Sixth Doctor was similarly forced to revert to all of his previous incarnations on Terra Nova. (PROSE: State of Change) The Tenth Doctor was once forced to retro-regenerate into his ninth self by an age-regression gun. (COMIC: The Fountains of Forever)