3. “The Tenth Planet”
The very first regeneration of them all! Could you imagine watching Doctor Who from the start and seeing the Doctor collapse, die, and turn into someone else without much warning at all? If only we could all have our minds wiped and go back and watch this for the first time. Without this regeneration, the show would have just been a little known cult show that ran from 1963-1966, and instead, we're celebrating it 50 years later.