With Infinity War (2018), Marvel Studios is about to begin the grand finale to the first major arc of its cinematic universe. The story that began in Iron Man (2008) will finally come to a conclusion. Seeds that were planted over 18 movies will finally come to fruition, at least according to Marvel Studios. While each film focused on an individual story, they were full of moments that set up future storylines, sometimes within a completely different franchise. This helped connect each of the films, but not all of these moments were entirely successful. In fact, Marvel dropped the ball quite a few times.

It's understandable. Planning out a project as massive as the Marvel Cinematic Universe involves a lot moving parts, and plans change. Sometimes, it's clear that Marel was setting up one thing, but then had to change course. The problem is that those in charge already set up the original idea. Other times, it seems like a director wanted to include a reference as an Easter egg to the fans, not realizing the impact and expectations they were setting. Either way, these moments ended up being cool at the time, but looking back, Marvel wasted a lot of opportunity with them.

• Iron Spider art in Feature Image by Sany Lebedev.

15 EGO'S PLANET FACE

It's not uncommon for comic book movies to redesign the weirder looking characters. For example, Arnim Zola appears as a giant computer screen instead of a robot in Captain America: The Winter Soldier (2014). When it was announced that Kurt Russell would be portraying Ego, the living planet in Guardians of the Galaxy: Vol 2 (2017), many assumed that a similar redesign would occur.

In the comics, Ego lives up to his name. He is a giant planet with a face (and a goatee, which is weird). In the film, Ego manifests a humanoid body to interact with the Guardians, although he is still technically a living planet. Except, in one scene it's revealed that the planet does have what appears to be a giant face. Unfortunately, the face on the planet never moved or spoke. Ego dies while still just manifesting as Kurt Russell.

14 SHIELD DISSOLVING

Captain America: The Winter Soldier (2014) really upped the stakes by revealing that Hydra had secretly taken over S.H.I.E.L.D., the world peacekeeping organization. By the end of the film, Cap and his team had defeated Hydra and revealed their secrets to the world. A consequence of this was the dismantling of S.H.I.E.L.D. Black Widow testifies before a senate committee about S.H.I.E.L.D.'s actions, and Nick Fury heads "underground."

While this had a big impact on Agents of S.H.I.E.L.D., it didn't really change anything in the movies. Maria Hill went to work for Stark, essentially serving in the same role. The CIA also stepped up, basically doing the same thing S.H.I.E.L.D. was known for. As for Nick Fury, he found a spare helicarrier and showed up to help fight Ultron.

13 FRIGGA DYING

One of the most criticized films in the Marvel Cinematic Universe would have to be Thor: The Dark World (2013). One of the major complaints about it is that nothing all that important happens. Which is weird, because it's the movie that first revealed that the Infinity Stones existed. In fact, the Aether is one of the stones. The events of this movie are hugely important for Infinity War (2018). Also, Malekith kills Thor's mom.

Of course, after Frigga dies, everyone moves on very quickly. As an Asgardian, she likely had another hundred years of life left in her. It briefly upsets Thor, but he's fine by the end of the film. Which, by the way, is only a few days later. Thor is more concerned about taking Jane Foster on a date than mourning his own mother.

12 THE DESTRUCTION OF THE BIFROST

Thor (2011) introduced Asgard to the Marvel Cinematic Universe, and revealed that Asgardians use the Bifrost to travel from world to world. During the finale of that film, Loki attempts to use the Bifrost to destroy Jotunheim, home of Asgard's one time enemies, the frost giants. Thor realizes that the only way to save Jotunheim is to destroy the Bifrost. This will, unfortunately, isolate Asgard from the other realms, and prevent Thor from reuniting with Jane Foster.

Thor destroys the Bifrost in what should have been a powerful and heroic moment. Unfortunately, it really didn't have that big of an impact. It turns out, Thor still travels to Earth for the events of The Avengers (2012). Asgard repairs the Bifrost just a few months later. Thor's heroic sacrifice was turned into a slightly less heroic inconvenience.

11 PEPPER GETTING INFECTED WITH EXTREMIS

Aldrich Killian kidnaps Pepper Potts and injects her with the Extremis virus in Iron Man 3 (2013). Pepper gains superpowers and ultimately saves Tony and kills Killian. The film ends with Tony saying that he'll solve the Extremis problem, since it had a tendency to cause the infected person to explode in a fireball.

In the comics, Pepper eventually gets her own armor and becomes Rescue. It seemed like the movies were setting Pepper up to become a superhero of her own. A cameo in Spider-Man: Homecoming (2017) reveals a non-exploded Pepper. So, what happened? Does she still have super powers? Or did Tony completely remove Extremis from her body? As far as the audience knows, she's back to being a regular, non-fire powered person.

10 CAP KISSING AGENT 13

Steve Rogers hasn't had much luck with the ladies. In Captain America: The First Avenger (2011), he meets and falls in love with Peggy Carter. Unfortunately, before they can be together, Cap crashes a giant plane into the arctic and is frozen for several decades. In Captain America: The Winter Soldier (2014), he develops a flirty relationship with his neighbor Sharon, but it turns out the she's an undercover S.H.I.E.L.D. agent.

Cap reunites with Sharon in Captain America: Civil War (2016), when he finds out that she's actually Peggy's niece. The two grow close, and Cap eventually kisses her. This seemed to be setting up a future relationship between the two, just like in the comics. Unfortunately, Sharon isn't set to appear in Infinity War (2018) or Avengers 4 (2019), which are set to be Chris Evans' final MCU appearances.

9 AGENT SITWELL NAME DROPS STEVEN STRANGE

Captain America: The Winter Soldier (2014) revealed that Hydra has infiltrated S.H.I.E.L.D. and plans to launch three heavily armed helicarriers. They've developed a program that will identify individuals that could potentially pose a threat to Hydra, and the Helicarriers target those people. Captain America captures Agent Sitwell, a Hydra mole.

During the interrogation, Sitwell mentions several of the individuals on Hydra's watch list, including Dr. Steven Strange. Fans were excited, as the was the first mention of the MCU Dr. Strange. If he was a target of Hydra, this implied that he was already working as the Sorcerer Supreme behind the scenes. Dr. Strange (2016) set his origin long after the events of Winter Soldier, which ruins this reference. Why was Hydra targeting some random surgeon, and why would Sitwell know his name?

8 QUICKSILVER'S DEATH

Joss Whedon loves to kill characters. In Avengers (2012), he killed off fan favorite Agent Coulson and used the death as the turning point to bring the heroes together. Fans expected that another hero would die in the follow up Age of Ultron (2015), also directed by Whedon. The film seemed to be setting up Hawkeye as the eventual victim, so it was a little surprising when Quicksilver died (taking a barrage of bullets meant for Clint).

While this momentarily enraged the Scarlet Witch, it ultimately hasn't had that big of an impact on the MCU in general. Wanda moved on from the death of her twin brother incredibly fast, and Quicksilver has basically been forgotten at this point. He's a major character in the comics, so killing him off so early on should've at least meant something a little bit more.

7 CAP NUDGING MJOLNIR

In Thor (2011), Odin places an ancient Asgardian enchantment on Mjolnir, which says that whoever is deemed worthy shall be able to lift the hammer and be granted the power of the Norse god of thunder, Thor. It's not clear if this enchantment was in place beforehand, but it's definitely in effect from that point forward. In Avengers: Age of Ultron (2015), Tony Stark decides to test his inherent worthiness, followed by the other Avengers (minus Natasha, who recuses herself).

None are able to lift it, but Captain America is able to nudge it. In the comics, Cap has lifted the hammer, and this seemed to be setting up an epic Mjolnir wielding Cap. Unfortunately, Mjolnir is destroyed in Thor: Ragnarok (2017), so Cap may never be more than "nudge-worthy."

6 TONY'S SUITS BLOWING UP

Iron Man 3 (2013) starts with the shocking image of Tony Stark's hall of armor blowing up. Each of his armor explodes into a fireball one at a time. Obviously, the movie was warning fans that things were about to get crazy. To be fair, Iron Man 3 does put Tony through the ringer, and he spends much of the film without his armor. Of course, it's later revealed that he had a legion of other armor safely tucked away, but those are also all blown up by the end of the film.

The next time Tony appears in Age of Ultron (2015), however, he not only has a perfectly good Iron Man armor, he also has the entire Iron Legion built. Tony lost all of his Iron Man armor, and the problem was resolved in between films. That's the definition of a let down.

5 LOKI REPLACING ODIN

Thor: The Dark World (2013) ends with one of Marvel's most shocking cliffhangers ever: Loki has replaced Odin on the throne of Asgard. Not only that, but he secretly kidnapped his father and is now masquerading as him, so no one even knows that Odin is missing. Even for fans that found The Dark World to be disappointing, this was an exciting development.

Then, nothing happens. Literally, there's no intrigue, no chaos, nothing. In Ragnarok (2017), Thor immediately reveals Loki's scheme and finds Odin. Sure, Odin then dies, but the movie makes it clear that he doesn't die because of Loki's magic. It's just Odin's time to go. Marvel put their most cunning villain on the throne of Asgard, and then all he did was put on a play starring Matt Damon.

4 SPIDER-MAN TURNING DOWN TONY'S OFFER

After spending most of Spider-Man: Homecoming trying to win Tony Stark's approval and a place on the Avengers, Peter Parker turns it down when he realizes that he needs to stay close to the ground. It's a huge character moment for Peter, and actually gets a positive response from Stark.

Then, in Spider-Man's very next appearance in Infinity War (2018), he joins the Avengers. So, it's cool that Peter had that moment of personal growth, but it's immediately undone. It's cool to see Spider-Man join the Avengers, but it undercuts the ending of Homecoming. It would've been better to see Peter on his own at least one more time before he joins the Avengers. It turns out, it didn't matter what Peter said to Tony, he was becoming the Iron Spider no matter what.

3 CAP'S AVENGERS GETTING ARRESTED

In Captain America: Civil War (2016), Steve Rogers forms a team of renegade Avengers to help clear Bucky's name. Due to the recently passed "Superhuman Registration Act," this puts them at odds with the actual Avengers, led by Tony Stark. Cap's team is eventually captured and arrested, and are jailed in the Raft, a high tech prison placed in the middle of the ocean.

The film ends with Cap breaking his team out of prison, but the Avengers are still splintered. For Cap's team, this means that they were imprisoned by their friends. It should be a huge breach of trust. Yet in the trailer for Infinity War (2018) shows the Avengers essentially back together. Members of Cap's team and Tony's team working together. Once again, a huge game changing development is undone before it can be fully explored.

2 TONY REMOVING THE ARC REACTOR FROM HIS CHEST

In Iron Man (2008), Tony Stark is forced to place an experimental arc reactor in his chest after an explosion leaves shards of shrapnel embedded near his heart. While he also uses this reactor to power his armors, it's main purpose is to keep him from dying. That is, until the end of Iron Man 3 (2013), when Tony decides that he's had enough and has the reactor and shrapnel removed from his chest.

This is a moment that could have completely redefined Tony Stark. Instead, it seems to have had no impact. Tony is the same character that he always has been. Without the arc reactor in his chest, Tony should have started looking at saving the world from a different perspective. Instead, he's still just building armor and being snarky.

1 TONY MEETING WITH GENERAL ROSS

Everyone credits Nick Fury showing up in the after credits scene in Iron Man (2008) as launching the shared universe, but the real credit goes to The Incredible Hulk (2008). The final scene of the movie shows Tony Stark meeting with General Ross to discuss the Avengers. This was the actual first moment when a character from one movie showed up in another franchise.

The problem is that this scene ultimately didn't lead to anything. It seemed to imply that Tony was actively looking for individuals for a team, and that he considered the Hulk a threat. Marvel later retconned the whole thing because it didn't fit with how they wanted the story to unfold in Avengers (2012). It was great to see characters coexist across films for the first time, but it would've been better if it actually led to something.