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 part four of the story. It was changed to the correct version for the BBC video release.
Oringally, The Sixth Doctor was to have regenerated at the end of this episode. 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 wanted to leave at the end of the fourth episode so he could have the whole story. 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).
The concept of creating a weapon by collecting the minds of all the great thinkers, including the Doctor's, was also used in the unfinished and unbroadcast story "Shada". Both stories involve the Doctor using his stolen consciousness to counteract the weapon.
One reason for the story's problems was that Pip and Jane Baker had no idea who would be playing the new Doctor or how he would be characterised - and, at least when they started work on the project, the series had no script editor for them to discuss things with.
In a behind-the-scenes interview featuring Sylvester McCoy, he jabbed at having to wear Colin Baker's over-sized wardrobe before switching into his Doctor's new clothes. Aside from donning the loud colours of his predecessor, the costume was tailored to Baker's height, 6ft (183cm), which loosely fit his smaller height of 5ft 6in (168cm). He humorously protested about "getting lost for three days" inside the floppy fabrics.
Sylvester McCoy protested about wearing the question mark jumper. It wasn't until his reprisal of the Seventh Doctor in Doctor Who (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) .
During the regeneration, the exercise bike the Sixth Doctor rides in "Terror of the Vervoids" is visible in the TARDIS control room. In Issue 409 of Doctor Who Magazine, in an article on regeneration, the writer suggests that the Sixth Doctor's "mortal" injury may have been caused by him falling off the bike. However, the explanation offered in the Big Finish story "The Brink of Death" gives the Sixth Doctor a dignified death and negates this possibility. The same can be said for the novel "Spiral Scratch", which was the first depiction of the regeneration until being re-designated as an alternate continuity by the release of the audio story.
Originally The Doctor was to regenerate at the end of the episode in an explosion. The Rani disguised as Mel tells The Doctor that he had regenerated in a explosion which gave him his post regeneration trauma.