New CGI title sequence was used for the first time, costing £20,000. The appearance of the Doctor's face was originally designed differently. It started as a skull build up developing into a head, but this was considered too sinister and dropped. However, it was accidentally broadcast with Time and the Rani: Part Four (1987). It was changed to the correct version for the BBC video release.
Originally, the Sixth Doctor was to have regenerated at the end of this serial. The script had The Doctor staying behind at the Rani's headquarters to ensure nothing went wrong with the missile strike. The ensuing explosion causes him to regenerate. Colin Baker agreed to a regeneration, only if he would feature in the whole of the season (not just one of four serials) and then leave at the end of the season. Neither party could come to an agreement, hence the Sixth Doctor's unceremonious demise.
Sylvester McCoy was the first actor to play two incarnations of The Doctor. In 1987, Colin Baker refused to film a regeneration sequence after being dropped from the lead role, so McCoy donned a blond wig and portrayed an unconscious 6th Doctor just prior to his transformation into Doctor #7. The second actor to play two different versions of the Doctor was Richard E. Grant, having played The "Quite Handsome" 10th Doctor in the BBC Comic Relief charity spoof Comic Relief: Doctor Who - The Curse of Fatal Death (1999). He then went on to voice the 9th Doctor in the BBC web animation Doctor Who: Scream of the Shalka (2003).
This is the first time The Doctor is seen regenerating at the beginning of a serial, as opposed to its end (barring recap footage, of course).
Sylvester McCoy protested about wearing the question mark jumper. It wasn't until his reprisal of the Seventh Doctor in Doctor Who: The Movie (1996) that his campaigning to discard the pullover was generously granted. He instead wore a red waistcoat (And was ironically "killed" before he could get any significant screen time wearing the waistcoat) .