While Marvel comics can often have violent moments, the Marvel Cinematic Universe tends to be family-friendly as it is owned by Disney. However, the movies are PG-13, so there are violent moments every now and then. There isn't any gore or overly-bloody sequences, but there are moments that will make moviegoers flinch.
The action in the MCU is phenomenal and it usually is able to portray large battles without featuring anything too disturbing. While characters do get killed or harmed, it's never shown in a graphic manner.
Thor Loses An Eye
Sibling rivalries can be intense but not usually as intense as the one between Thor and his sister Hela, the goddess of death. Hela is an immensely powerful god who not only killed all of Thor's friends, but also left Loki and Thor stranded out in space.
She can also make knives appear out of thin air and is a great fighter. In the final fight between Thor and Hela in Thor: Rangarok, Thor suffers a nasty hit when Hela slashes him across the face, knocking out an eye. Thor would later get a replacement eye from Rocket but it still made audiences wince when his eye was knocked loose.
Kaecilius Decapitates A Librarian
Scott Derrickson is known for directing horror films and immediately begins Doctor Strange with some light horror violence. Kaecilius and his henchmen infiltrate the Kamar-Taj library to steal the Book of Cagilostro. Before they stole the book, the group restrained the librarian before Kaecilius decapitated him with a pair of daggers.
What's disturbing is the precision in which Kaecilius performs this along with his casual expression suggesting he shows no remorse for his actions. The decapitation itself is shown via shadow, but the implication of it is rather gruesome, especially for an MCU movie.
Thanos Kills Loki
In the beginning of Avengers: Infinity War, the Russo brothers wanted to prove Thanos means business. He certainly did as Thanos kills Loki, one of the most manipulative and popular villains in the MCU. Even though Loki has been a villain for such a long time, his recent actions in Thor: Ragnarok made him a more likable character and he had always been a fan-favorite.
It was tough to watch Thanos choke the life out of Loki and the Russo brothers didn't shy away from showing the whole thing. It was a strong way of showing just how intimidating Thanos is.
Iron Man Opening Sequence
The first scene of the MCU in Iron Man began with a bang. Several bangs, in fact. While driving around with a group of the armed forces, Tony Stark and the group are attacked by a terrorist group who are utilizing many of Stark's weapons.
While this scene isn't bloody, the group of soldiers Tony is traveling with are killed off rather quickly and brutally. Tony also suffers an injury after a bomb lands next to him, with some of the shrapnel injuring him. The MCU doesn't feature much of intense war violence seen in many war movies, but this opening set up the MCU in a mature and gritty way.
Thanos Stabs Tony Stark
This scene had every Marvel fan gasping during Avengers: Infinity War. After Tony gave Thanos a decent whooping, Thanos proved that it really didn't matter after he snapped off a piece of Tony's armor and stabbed him with it. It's a shocking and heartbreaking scene that had the audience begging for Tony to live.
The Avengers battle against Thanos on Titan is epic, but Thanos proved that he is an almost unmovable force. Luckily, Tony got his revenge on Thanos at the end of Avengers: Endgame, even if he had to sacrifice his own life to do it.
Ultron Cuts Klaue's Arm Off
In Avengers: Age of Ultron, we are introduced to Andy Serkis' insane, bumbling Ulysses Klaue. While he isn't in the movie for long, he is featured in negotiations with Ultron to buy stolen vibranium.
Klaue manages to annoy Ultron, who then proceeds to brutally chop off Klaue's arm. Klaue should thank Ultron because the mechanical arm powered by vibranium he has in Black Panther is a lot cooler than a regular arm. In Age of Ultron, this scene was treated for laughs and while the MCU has lots of hilarious moments, this isn't really one of them.
Loki Takes An Eyeball
In The Avengers, Loki goes to steal iridium with the mind-controlled assistance of Hawkeye. In order to get into the facility, Loki needs optical identification from someone who works there.
Loki uses a device that is able to harness someone's eyeball and transfer a hologram to Hawkeye. He abruptly interrupts a fancy museum party and viciously takes an eye from one of the workers. During this scene, Loki can't help but smile at all of the chaos he's causing. The orchestration makes this scene seem much less brutal than it is, but the man's writhing and sound effects make this scene disgusting.
Killmonger And T'Challa's Duel
Killmonger is a ferocious fighter and his first duel versus T'Challa proves Killmonger is a fierce opponent with nothing to lose. He attacks T'challa with brutal punches and slices and stabs to take him down. T'Challa grossly underestimated his opponent and everything Killmonger has been through.
His determination and ferocity led Killmonger to best T'Challa. In this scene, he also kills Zuri, stabbing him in the chest. The fight ends with Killmonger throwing T'Challa off of a cliff into the running river below. While T'Challa does later get payback, it is tough to watch the Black Panther struggle during this fight.
Thor Kills Thanos
Thor finally went for the head. It surprised a lot of people when Thor chopped off Thanos' head in the beginning of Avengers: Endgame. While Thanos ended up being the main villain, many were expecting the version of Thanos from Infinity War to remain alive for this movie as well.
Thor felt a deep level of regret after failing to kill Thanos before he wiped out half of the universe and killed Thanos in a fit of rage. It's cool to see Stormbreaker in action and Thor certainly packs one heck of a swing.
Winter Soldier Kills Tony Stark's Parents
Before the final fight in Captain America: Civil War, Zemo reveals to Tony Stark that Bucky Barnes, aka the Winter Soldier, assassinated Tony's mom & dad. While Bucky wasn't in control of what he was doing, it's still understandable why Tony became so enraged. The scene is brutal as well with Bucky delivering a staggering punch to Howard Stark.
Bucky also chokes out Tony's mom with a disturbing, emotionless expression. The following fight is so emotionally investing because despite killing Tony's parents, we understand that Bucky wasn't in control of his actions and we don't want Tony to kill him.