The budget for this mini-movie allowed for far more elaborate sets than had been seen since the first The Black Adder (1982). In particular, the set for "Queenie" Elizabeth's court - a small room, barely capable of holding 10 people in Black-Adder II (1986) - is a large, richly-decorated space in this film, filled with dozens of courtiers. Queenie's costume is also far more elaborate in this film.
This film includes extensive location shooting, a rarity for a "Blackadder" production. Although the first series (The Black Adder (1982)) did quite a bit of location shooting, the high cost nearly led to the cancellation of further series. After extensive cost-cutting, Black-Adder II (1986) includes the only location shooting in later series/specials: a courting scene in Black-Adder II: Bells (1986), and the end credit sequences, all filmed in a single day at Wilton House, Wiltshire.
Brian Blessed, Elspet Gray and Robert East were originally going to reprise their roles from The Black Adder (1982). The scene would have been Blackadder and Baldrick arriving at Bosworth field and killing Henry Tudor with the time machine, however the scene was later changed to the battle of Waterloo as Blessed was unable to reprise his role of Richard IV.
Although not correct to the period, black extras can be seen in the Robin Hood and Elizabethan scenes. This is because of a long-running joke between comedians Richard Curtis and Lenny Henry who apparently always complains that he could have been the extra instead.
Baldrick's line about how "there's always a Blackadder and there's always a Baldrick" is a reference to the fact that those are the only two characters who have appeared in every single incarnation of Blackadder.
In addition to playing the various incarnations of Melchett, Stephen Fry reprises his role as the Duke of Wellington, though the character bears little resemblance to the version who appeared in 'Blackadder the Third.'
The trivia items below may give away important plot points.
Regarding Blackadder's cunning plan to become king, Baldrick asks if it is as 'cunning as a fox what used to be Professor of Cunning at Oxford University, but has moved on and is now working for the UN at the high commission of International Cunning planning?'. This is building on a line delivered by a previous Blackadder to his Baldrick in Blackadder Goes Forth: Goodbyeee (1989), involving a plan 'as cunning as fox who's just been appointed Professor of Cunning at Oxford University'
Blackadder comes back with Shakespeare's autograph. This is likely an in-joke regarding the lack of any known William Shakespeare autographs in reality, which have led some to speculate that Shakespeare was illiterate and wrote through dictation - a notion dismissed by the more intense scholars of his life.