; Date: January 6, 2020
The Master is an embodiment of evil, and Skyfall 2 certainly demonstrated the current Doctor Who show runners remember this. The Master's violence in this episode echo's earlier examples of The Master. The earliest appearances of The Master up until today had him committing crazy acts of violence and power grabbing monstrosity. He would team up with any baddie, develop crazy technological gadgets of destruction, and spawn schemes that often would have resulted in the destruction of whole planets.
Someone coming to Doctor Who as a new viewer might be aghast at what we saw in Skyfall and Skyfall 2. Here's a guy we were initially led to believe was a good guy, but then it became clear he had no regard for humans, and was leading a crazy scheme to take over Planet Earth for some unknown scheme. And along the way The Master wanted to off The Doctor, because the two have been in a feud for thousands of years.
The Master and The Doctor represent the good-evil-twin archetype. If you will, if The Doctor is Sherlock Holmes, The Master is Moriarty. They were childhood friends, but when The Doctor headed off to visit the universe The Master headed off to destroy the universe.
For example in the 4th Doctor episode Logopolis, The Master wontonly killed two people just because they happened to wander by:
In this case the police officer was simply passing by and needed to call in using the police telephone box along the road. But the Master had materialized his TARDIS around the telephone box, then killed the police officer just because. The woman was Tegan's aunt, who was trying to repair the flat tyre on her car, but was caught by The Master and killed. He used his tissue-compression device to squeeze their bodies down to this small form. The only purpose this used in the episode was to leave a kind of calling card to The Doctor, that indeed The Master had escaped from Traken, and that The Master was continuing to perform evil deeds.
So when The Master burst into the armaments exhibition where The Doctor had materialized, he started killing people just to get The Doctor's attention:
Yes, it looks all posh and British Empire, but strip all that away we have a villain and a good-guy, with the villain seeking to provoke a reaction from the good-guy. Of course "guy" in this case is incorrect, but you get the point. It's like taking a punch at someone just to provoke a reaction, but in this case there were several dead bodies.
And, that's The Master's typical course of action. For example as Missy, The Master froze all airplanes around the world just to get the attention of U.N.I.T. and Clara so they could track down The Doctor. In other instances The Master would hypnotically control someone, use them for a nefarious scheme, and dispose of them without a thought. In Skyfall 1 when The Master showed the compressed person whose place he took (in a matchbox, an homage to an earlier Master victim), The Master casually tossed aside that dead body like it was nothing, again just like earlier incarnations of The Master.
In Capaldi's final season, the entirety of that season was spent with The Doctor keeping Missy locked in the dungeon trying to help Missy/Master heal:
That episode arc had The Doctor saving Missy/Master from a certain death by a cult of executioners. The Doctor's agreement to do so was to keep Missy/Master locked up for 1000 years (or more). But The Doctor had a different intention, to work on redeeming Missy/Master. He kept Missy locked up for maybe 70 years, while hanging out at an English University teaching a course on the nature of reality.
That season arc ended with The Doctor sending Missy into a tricky situation that turned out to be another insane scheme of The Master. It turned into a Two Masters story where Missy and The Master joined together to some degree in building a Cyberman army. Not just any Cyberman army, but the Mondas Cyberman army.
Great move, Doctor, to let your soft heart go kerflippity-floppy and release Missy early only to have it all go to heck.
In any case the ultra-violence of this new Master may have to do with the manner of Missy's death. It's not said in the story, but this new Master is probably the regeneration of Missy, and Missy's death was a serious betrayal. Hence the violence of this new Master must stem from that betrayal.
Or, maybe there's something else. At the very end of the story The Master says that he destroyed Gallifrey because of having learned about a deep lie buried in the Time Lord race.
The Master's own history is tied up in a betrayal of him personally by The Time Lords, a betrayal that was referenced in Skyfall 2. Namely - at some point of The Time War, the supreme council of the Time Lords (at that time led by Rassilon himself) determined one possible way to escape the Time War. This required going back to The Master's childhood and inserting a signal - four drumbeats - into his consciousness. The constantly repeating pattern of four beats caused him some madness and is a large part why The Master committed crazy acts.
In Skyfall 2, The Doctor used a Morse Code set to send out a series of four "dots". That's not legal by Morse Code, but is as The Doctor said a personal code between the two of them. The four dots referred obviously to the four drumbeats the Time Lords entered into The Master's consciousness.
In Skyfall 2 that was followed by the Doctor and The Master meeting at the Eiffel Tower, and The Master mentioning the Jodrell Bank episode. That refers to the culmination of the episode Logopolis mentioned earlier.
In any case - The Master suffered one betrayal from The Time Lords with that drumbeat pattern. During the episode in which we learned about this, the Master roared with indignation at the Time Lords attacking Rassilon personally looking like he went out in a blaze of glory and personally sending Gallifrey and the Time Lords back into the hell of the Time War.
That's the depth of betrayal The Master felt at that time. So ... in this episode we learn that The Master learned of another betrayal, not just of himself but the whole Time Lord race, and as a result he destroyed Gallifrey.