The final episode of the 1982 story "Earthshock" ended with the death of a continuing character. The closing credits for that episode were silent - the only time in the history of the series that this was done.
In a number of 1980s episodes, recurring villain The Master often first appeared in disguise. Actor Anthony Ainley was credited under a pseudonym on these occasions (usually an anagram of his own name) in order to preserve the element of surprise.
The tradition of showing The Doctor's face in the opening titles was not introduced until Patrick Troughton's tenure with the program was under way. During Jon Pertwee's era, the producers experimented with changing the opening credits and music. One of the rejected opening credits was accidentally included on some prints of the story "Carnival of Monsters" that were broadcast overseas.
For the first several seasons, each individual chapter (episode) carried its own title. This practice was abandoned following the 1966 story "The Gunfighters." As a result, several early stories are known by several different titles.
While several episodes made use of teaser sequences before the opening credits (though only a handful in the show's 26-year history), the 1970 7-part story "The Ambassadors of Death" was unique in that it was an experiment in changing the format of the opening credits that was not repeated. At the start of each chapter, the credits would begin as usual but end right after the title "Doctor Who" appeared (before the episode and writer titles appeared). A brief teaser then followed, followed by the remainder of the opening sequence, as usual. Another story from the same season, "Inferno", also altered the format of the opening credits slightly by showing the episode and writer titles over footage of bubbling lava.
For most of the Hartnell era, the episode title appeared superimposed over the first scene (after the title sequence had completed). Later, and continuing on occasion during the Troughton era, the episode title and writer credit would be presented in a unique format (i.e. in the form of a computer print-out for "The War Machine", for example). When the opening credits were redesigned during the Troughton era (and now incorporated an image of the Doctor's face), the episode title and writer credit were usually included during this sequence.