Peter Davison has joked on several occasions of how he was "upstaged" by Nicola Bryant in his last major scene as the Doctor. Before the regeneration hallucination occurs, Davison is lying on the floor and his head is resting by Bryant, who is kneeling beside him. As he is delivering his last few lines, Bryant's loose fitting outfit prominently displays her cleavage.
Colin Baker's girth was too great to properly fit into Peter Davison's costume, and so he was forced to give his performance with the trousers undone - permitting him the opportunity to moon Davison's wife, actress Sandra Dickinson.
The Fifth Doctor's regeneration, like the Fourth Doctor's, features a flashback of that incarnation's companions. However, for this regeneration, it was decided that special recordings of the Fifth Doctor's companions would be used instead of stock footage. This required Matthew Waterhouse, Sarah Sutton, Janet Fielding, Mark Strickson, Gerald Flood and Anthony Ainley to return in cameos for the regeneration sequence. Fielding, Strickson, Flood and Ainley were already under contract to appear in the stories of Season 21. However, special contracts had to be made for Waterhouse, who left the series in Season 19, and Sutton, who left in Season 20. Johnny Byrne, who created the character of Nyssa in The Keeper of Traken had to be paid royalties for the use of the character in the regeneration scene.
The closing credits feature the face of new Doctor Colin Baker and list him before Peter Davison. Davison's tenure seems to come full-circle in this case: Doctor Who: Logopolis: Part Four (1981) (his first physical appearance in the series) also gave him second billing in the credits.
As the Doctor carries Peri back into the TARDIS at the end of the story, he flinches at a nearby mud burst. This is because the explosion was prematurely triggered by the technicians, shooting sand into Peter Davison's eyes and forcing him to recoil in pain.
This story is notably one of few where the eventual outcome negates the importance of the plot. The Doctor's role provided no historical accomplishments, and instead caused an inadvertent massacre, a gigantic power collapse, and even his own "death", all of which could've been prevented had the Doctor never gotten involved (or even went to Androzani Minor, for that matter).