In a story pitting good against evil, heroes against villains, or even just something with a conflict of any kind, you can usually expect the protagonist to come out on top. Depending on the situation, such protagonists may be forced to get their hands dirty in order to win.
Yes, there may be exceptions, but heroes in movies do kill. It's part of the job, and their fight wouldn't be particularly heroic if it were easy, but sometimes they get a helping hand from the other side.
This isn't quite 'the enemy of my enemy is my friend', and you wouldn't expect to see the Caped Crusader taking the Joker out to lunch for disposing of a Gotham criminal on a permanent basis, but villains do kill other villains. It's a dog eat dog world on the wrong side of the tracks, after all.
Whether one villain got in the way of another, a temporary alliance came to the end of its mutual benefits, or a good old classic case of revenge, villains kill villains, and usually in the most brutal of ways.
10. Surtur Killed Hela - Thor: Ragnarok
There were a handful of different villains that Thor went up against in his third solo movie back in 2017. Although Loki was arguably more hero (or at the very least anti-hero) than villain by this point, there was still Surtur, Hela, and her executioner, Skurge.
The former was utilised right at the beginning of Ragnarok, seemingly more as a plot device connecting the journey Thor began in Age of Ultron to his eventual return to Asgard. It also served as a quick reminder of how awesome the God of Thunder was with Mjolnir in hand, as if anyone needed reminding.
It seemed as though Surtur was to be another secondary villain who wouldn't be seen past the first act in the MCU, and yet, he made his triumphant return right at the last when Loki plunged his crown/giant eyebrow into the Eternal Flame in Odin's vault.
The fire demon grew to the size of a mountain and destroyed not only Asgard, as Ragnarok prophesised, but he destroyed Hela as well. Thor was absolutely no match for his big sister, and so enlisting the help of the monster whose arse he kicked at the very beginning of the film was the only way to take her down.