Timeslip

Timeslip is a two part story by Dez Skinn and Paul Neary, from Doctor Who Weekly #17-#18 (6th February-13th February 1980). Essentially a space filler, it is significant in that it introduces the idea of retro-regeneration; when the TARDIS is captured by a mindless space amoeba which feeds on time energy, The Doctor finds himself regressing back through his former incarnations until his first incarnation finds a way of overloading and destroying the creature. Though the second and third Doctors appear only briefly, this is nonetheless the first multi-Doctor story to appear in comics.