Marvel Studios changed the superhero movie landscape with 2008's Iron Man. The film's critical and financial success opened the door for the MCU. Now, ten years, 18 installments and over $13 billion later, the MCU is one of the most popular and beloved series out there. Putting great storytelling and compelling characters aside, one thing that's made the franchise so attractive for general audiences is its family-friendly nature.

Making a superhero film that appeals to everyone isn't easy. Studios and directors need to deliver movies with mature enough storylines to please adults, while also embracing the lighthearted and adventurous spirit of comics to appeal to children. Throughout the years, Marvel Studios has balanced those two aspects perfectly. They're fun, action-packed tales that allow grown-ups to have fun while giving children exciting heroes to look up to. Regardless of whether you want to watch Guardians of the Galaxy, Captain America: Civil War, or Spider-Man: Homecoming, the films are guaranteed to be a blast for people of all ages. However, while the MCU is suitable for all types of audiences, plenty of its movies haven't been afraid of pushing their PG-13 rating from time to time. With that in mind, here are 15 times that MCU movies seriously pushed their kid-friendly ratings:

15 TONY STARK'S ABDUCTION SCENE

Iron Man cemented Tony Stark as a pop culture staple and laid the groundwork for what the Marvel Cinematic Universe would become. Despite kickstarting the MCU, however, the movie had a considerably more mature tone than what we've seen from the franchise in recent years. This was made clear in the very beginning, as the film opened with Tony Stark having fun with three soldiers escorting him back to a military base.

Unfortunately, their fun banter was cut short by a ruthless ambush courtesy of the Ten Rings.

The scene didn't pull any punches with its depiction of war, showing three soldiers getting gunned down mercilessly while a desperate battle developed in the background. Overall, it would have been easy to mistake this scene for a sequence from a mature war drama due to its hard-hitting realism and considerable violence.

14 KAECILIUS BEHEADS A LIBRARIAN

In 2016, Doctor Strange got the chance to shine in his very own film, where he had to defend Earth from Kaecilius, a sorcerer looking to bring Dormammu into our dimension. The baddie wasn't incredibly well developed, but that didn't stop him from being one of the most violent adversaries in the MCU. At the beginning, Kaecilius and his followers broke into Kamar-Taj and went into the Ancient One's library to steal the book of Cagliostro.

There, the villain encountered the library's keeper and dispatched him in a rather stomach-churning fashion. After his followers tied up the keeper by his wrists and ankles, Kaecilius severed his head. The beheading was shown in a shadow, and the sound of the head hitting the bucket beneath the keeper's body made the scene all the more unsettling. Fortunately, Wong didn't encounter the same fate once he took on the job of librarian.

13 TONY STARK GETS DRUNK WITH FLIGHT ATTENDANTS

It shouldn't come as a surprise that the billionaire, playboy, philanthropist has more than one entry on this list. The morning after sleeping with Christine Everhart (and a day before his capture), Tony flew out with his best friend, James Rhodes, to present a new weapon to the military. During their flight, Rhodey decided to scold Tony over his irresponsible nature. Unsurprisingly, Stark was having none of it.

Instead of listening, the billionaire started to drink and quickly got Rhodey drinking as well.

At first, the sequence seemed like just a playful conversation between the two friends. Surprisingly, things took a sharp turn when the scene cut to Tony and Rhodey completely drunk on a couch, blabbering as they watched flight attendants dancing around a pre-installed airplane pole. That kind of scene may be expected in Deadpool, but it definitely isn't in an MCU movie.

12 HULK AND ABOMINATION'S BRUTAL BATTLE

The Incredible Hulk established Bruce Banner in the MCU. In the film, Banner was pitted against Emil Blonsky, a special agent who was injected with a version of the Super Soldier serum. The serum affected Blonsky's mind and he became obsessed with Hulk. After some experimentation, Blonsky turned into the Abomination and started wreaking havoc around Harlem.

Hulk went there to stop him, and their encounter completely embraced the brutality of the Jade Giant. Their fight got particularly gruesome toward the end. Abomination punctured Hulk with one of his elbows, and the hero got him back by removing one of those bones and then stabbing him in the chest with it. To top all that off, Hulk almost strangled the Abomination to death with a chain. To this day, it's difficult to find another Marvel fight that comes close to the violence depicted in this movie.

11 IVAN VANKO KILLS TWO GUARDS BY HANGING

Despite its polarizing reception, Iron Man 2 did a great job introducing one of Tony Stark's most dangerous foes, Ivan Vanko. Ivan -- the son of a disgraced scientist who worked with Howard Stark -- made it his mission to ruin Tony. To accomplish this, he allied himself with Justin Hammer. Vanko showed how ruthless he was several times throughout the movie, but one of those instances was particularly intense for a PG-13 superhero blockbuster.

At one point, Hammer realized that he was being played by Vanko, so he locked him in an office and placed two guards to keep an eye on him.

Sadly, things didn't go well for the Hammer employees. Vanko hung them together, and kept their dead bodies in front of his desk. It was an impactful image, one that let audiences know that Ivan was a formidable adversary, in and out of a mechanical suit.

10 LOKI TAKES OUT A PERSON'S EYE

In 2011's Thor, Loki achieved most of his mischievous deeds by using his wits and silver tongue, but in The Avengers, he got considerably more physical. Naturally, this resulted in quite a few violent acts from the God of Mischief, with one in particular really pushing the tone of the average superhero film. After attacking S.H.I.E.L.D. and mind-controlling several agents to do his bidding, Loki traveled to Germany to find a scientist who possessed an element he needed to stabilize the Tesseract.

Loki eventually marked his target, dragged him across the room and flipped him over a sculpture. With his prey subdued, the God of Mischief took out a device, and proceeded to take out the man's eye. The sequence was quite disturbing on its own, but Loki's deranged smile and heavy breaths made the moment all the more frightening.

9 TONY STARK'S ENCOUNTER WITH A REPORTER

The Tony Stark we know now is a composed individual looking out for mankind's best interest, but that wasn't the character we were first introduced to. In 2008's Iron Man, Stark was just a rich individual looking to spend his money, drink copious amounts of alcohol and sleep with as many women as possible.

Part of that extreme lifestyle was represented with a peculiar steamy scene in Stark's first solo adventure.

Before stepping into his limo following a hard night of partying, Stark is approached by reporter, Christine Everhart, who wants to discuss his role in developing weapons. The scene cuts abruptly, and we're taken to Stark's bedroom, where we see Tony and Christine kissing (apparently drunk) before falling off the bed, laughing. While the sequence wasn't particularly explicit, it was definitely not the sort of scene one would expect to be in a family-friendly superhero movie.

8 LOKI CUTS OFF THOR'S HAND

The Thor franchise has mostly shied away from depicting gruesome violence, but it has had its exceptions. One of the biggest examples can be found in 2013's The Dark World. In the film, the God of Thunder encountered Malekith, a Dark Elf hellbent on using the Power Stone to destroy Asgard. Due to the creature's power and enormous army, Thor was forced to join forces with his treacherous (and psychopathic) half-brother, Loki.

Both brothers traveled to another dimension to face Malekith, and right before they confronted the baddie, Loki seemingly betrayed Thor, cutting off his right hand. Surprisingly, the hero's maimed arm wasn't hidden or disguised. Instead, the shot allowed viewers to get a good look at the inside section of the God of Thunder's limb. Admittedly, the whole thing was later revealed to be an intricate illusion by Loki, but it's still some shocking imagery, especially for young children.

7 ULTRON CUTS OFF ULYSSES KLAW'S ARM

Yet another severed member on this list. Avengers: Age of Ultron set up a lot of exciting things for the future of the MCU. One of those elements was Ulysses Klaw, a prominent adversary in the Marvel Universe. In the sequel, Ultron sought out Klaw to purchase vibranium to build his brand new body. Their transaction seemed to be going smoothly at first, with Ultron paying his benefactor billions of dollars for his troubles.

Unfortunately, things went awry when Ulysses asked Ultron whether he was working for Tony Stark.

Unsurprisingly, Ultron became furious and in a fit of rage cut off Klaw's arm. Unlike Thor: The Dark World, nothing was shown. However, blood sound effects were added, giving audiences a pretty good idea of what was happening with the villain's severed limb.

6 DRAX'S CONVERSATIONS

In the first Guardians of the Galaxy, Drax was a warrior of few words, focused completely on killing the people responsible for murdering his family. That attitude changed by Vol. 2, though. Drax was much more more talkative, and he had fun making some rather explicit comments throughout the film. Shortly after capturing Nebula, for example, the Destroyer began describing his deceased wife to Peter Quill, and stated that her cold demeanor made his "nether regions engorge."

Then, when the Guardians traveled to Ego's planet, Drax asked their host whether he made certain parts for his human body, and proceeded to happily reveal that his father would tell the story of how he impregnated his mother every single year. As if that wasn't enough, he told Mantis that he was imagining being with her physically to make himself uncomfortable.

5 YONDU SLEEPS WITH ROBOTS

Yondu and the Ravagers made their MCU debut in Guardians of the Galaxy. While they were formidable adversaries, they weren't really fleshed out. In fact, they mostly acted as a foil for our main group of a-holes, chasing them across the galaxy to retrieve the Power Stone.

Fortunately, the merry band of mercenaries got the chance to shine in Vol. 2, and the sequel pulled no punches when depicting their very mature lifestyles.

When we first catch up with them near the beginning of the film, Yondu is shown inside what looks to be a hotel room, getting dressed after "being" with several robots. It was a particularly explicit depiction of his rogue lifestyle, and one that audiences probably didn't expect to see in a family-friendly franchise like the MCU. Nonetheless, it was a great way to establish the dirty environment the Ravagers lived in.

4 BUCKY KILLS MARIA AND HOWARD STARK

Sebastian Stan the Winter Soldier

Putting the Sokovia Accords aside, Civil War's main story drive was Bucky Barnes' struggle to distance himself from Hydra's evil deeds. This underlying conflict paved the way for one of the most haunting scenes in the MCU yet. In the film, it's revealed that the Winter Soldier killed Maria and Howard Stark. Not wanting to leave fans in the dark about what happened, the movie showed Bucky murdering the Starks in a particularly gruesome fashion.

The brain-washed assassin first killed Howard by pummeling his face with his metal arm. After that, he approached Maria and choked her to death. With both husband and wife gone, Bucky left. Now, keep in mind that the brutality of the scene wasn't gratuitous. It helped illustrate the gritty nature of the Winter Soldier and it perfectly set up Tony's moral conflict with Captain America.

3 HELA PLUCKS OUT THOR'S EYE

Thor: Ragnarok breathed new life into the Thor franchise by embracing a more comedic approach. Still, despite its playful nature, the movie had one gruesome moment that most likely raised its fair share of eyebrows. After punching and shooting his way out of Sakaar, Thor traveled to Asgard to confront his long-lost sister, Hela. The two siblings battled it out in Odin's throne room, but unfortunately for Thor, Hela proved to be a superior fighter.

After gaining the upper hand, the villain took her spear and plucked out Thor's right eye with one well-timed swing.

The opened eye socket and blood surrounding it was difficult to look at. Yes, the sequence wasn't as bloody as your usual R-rated action film, but it was still not the type of injuries we're used to seeing in the family-friendly comic book genre.

2 RONAN MURDERS A XANDARIAN

Guardians of the Galaxy is considered one of the funniest installments in the MCU and the superhero genre as a whole. However, it still had its fair share of adult moments. One of the most impactful ones came near the beginning of the film, courtesy of Ronan the Accuser. In his very first scene, the villain confronted a captured Nova Corps soldier as part of his revenge on Xandar. After having had enough of their conversation, Ronan murdered his prisoner with a direct strike to the head.

What made the scene even more uncomfortable was seeing the blood of the soldier running across a structure that led straight into Ronan's resting chambers. While not explicitly stated, it's easy to assume that the villain slept submerged in the blood of his victims. And just like that, Ronan was established as quite the force to be reckoned with.

1 PETER QUILL COMPARES HIS BODILY FLUIDS TO ART

Guardians of the Galaxy appealed to audiences of all ages. Even with its kid-friendly approach, however, director James Gunn sneaked in a mature joke that probably had some parents raising their eyebrows. Shortly after breaking out of the Kyln, Peter Quill, Gamora, Drax, Rocket and Groot boarded the Milano and flew away to meet with The Collector.

Their ride together proved to be anything but pleasant though, as their distinctive personalities instantly started to clash.

Following a brief disagreement, Gamora remarked that Quill's ship was filthy and left. Peter replied that if he had a black light, the Milano would look like a Jackson Pollock painting. As proven by other entries on this list, the MCU doesn't have a problem with innuendo, but Star-Lord's joke definitely pushed the limits of what we'd heard before in the franchise.