Okay, let's see if there's some more participation with this one. This is about characters returning to the series, whether it's an old companion coming back, or a re-visit from (or to) a supposedly one-off guest character. Main show and spin-off TV shows qualify. As per usual, entries should not be larger than 200x200 pixels and/or 1 Mb, and since Torchwood qualifies as a source, I want to remind you to keep your entries worksafe. Now, maybe let's start with one entry per user, maybe that will get some more people to participate.
My initial instinct was that we did that as a different contest, already, but then I reminded myself that I want people to participate. So, sure, bring it. My own entry: Billie Piper returns as Rose Tyler in "Partners in Crime".
Nicholas Courtney returns as Brigadier Alistair Gordon Lethbridge-Stewart (Retired) in Mawdryn Undead:
Since I rarely enter the Whovian contests, I didn't know. This is the entry I had in mind: Jacqueline Hill returns as High Priestess Lexa in "Meglos".