At the end of the day, a villain is a villain, and for them to end up turning on those who claim to share that title maybe shouldn't be as surprising as it often is.
Most of the time, obviously, it's you, the player, that they're really after, and they're not about to let anyone else get in the way of their goals, whatever that entails. On the flip side, sometimes it's you that's poked your nose where it shouldn't be; a place where the bosses have bigger axes to grind with each other than with you.
Whether it's satisfying or anticlimactic watching a heavily built-up foe snuffed out by someone other than yourself, it's almost always totally unexpected, and why we tend to assume that villains have some sort of universal code of honour is anyone's guess. Because in reality, they don't - and where they're concerned, the enemies of their enemy are certainly not their friends.
Now that bosses are killing other bosses, will video game heroes soon be out of a job?
10. Darth Vader - Star Wars Jedi: Fallen Order (2019)
Set between the events of Revenge of the Sith and A New Hope, it was probably inevitable that the writers of Star Wars Jedi: Fallen Order would find a way to shoehorn Darth Vader in there somewhere. The iconic series baddie makes his appearance at the very end of the game, in the imperial moonbase Fortress Inquisitorius.
When Cal Kestis defeats Trilla, the Second Sister of the Inquisitors, Vader appears behind her with all the appropriate smokey ambiance to confront her about her failure. And, as his track record mandates, he expresses his disappointment with one swing of his lightsaber, killing Trilla and then turning menacingly towards the player.
"Oh my god, I get to fight Darth Vader?!" you're probably squealing at this point. Well, yes and no. The stage is absolutely set for a boss fight, and you're free to wale on him all you like once the cutscene ends...but you'll discover very quickly that there's a distinct lack of a health bar for your armoured adversary, and none of your attacks will ever land.
Yep, the fight is unwinnable, and soon transitions into a scripted escape sequence. But the epic setup and deception of the encounter still totally counts in my books.