Even those who are wild about the Worlds of DC and sanguine about Sony's Universe of Marvel Characters have to give credit where it's due to Marvel Studios. They may not have invented the cinematic shared universe (arguably the Universal monster movies did that) but they sure perfected the formula. Such an exercise in long form storytelling has never been attempted before. While detractors may warn that the  bubble will burst at any minute, the Marvel Cinematic Universe's star continues to rise. The success and longevity of the MCU is the rising tide that raises all ships. The diversity of those films has helped to redefine exactly what a comic book movie is, while keeping interest in superhero cinema alive and well at the multiplex.

Yet, while even the staunchest DC purist must grudgingly tip their hat to Marvel Studios' massive accomplishment, even the mighty MCU has its imperfections. As the universe grows ever larger and more expansive, it has necessitated the abandonment of plot points throughout the series' 10 year history. They linger still, dangling and unresolved. An itch that movie buffs, and especially the Marvel comics literate, can perceive yet never scratch. Across the films and TV shows of the MCU there have been many characters, relationships and narrative opportunities that were teased yet never capitalized on. While we can't say for sure that they'll never be resolved (whoever would have thought Thunderbolt Ross or The Red Skull would return) it seems unlikely. It's likely that next year's Avengers 4 will usher in the winds of change across the MCU. Thus, it's likely that these 20 teases are forever condemned to go nowhere...

20 COSMO THE SPACEDOG

Cosmo the Spacedog

Whatever your thoughts on the controversies surrounding James Gunn, none could argue that he didn't nail the cosmic oddity of the Guardians Of The Galaxy title. The script (originally by Nicole Perlman and redrafted by Gunn) borrowed heavily from Dan Abnett and Andy Lanning's seminal run on the title which began in 2008.

That run features a wide array of wacky characters including a telepathic Soviet spacedog named Cosmo. While the character (created by Abnett and Lanning) features heavily in the comics, he was disappointingly relegated to a cameo in the first movie that you might've missed if you blinked. With such uncertainty surrounding the franchise's third instalment it seems unlikely that we'll ever see this little guy again.

19 THE 'REAL' MANDARIN

all hail the king

It's been five years since the release of Iron Man 3 but Marvel fans are still divided when it comes to the Mandarin reveal at the end of the film's second act. The revelation that the imposing Mandarin promised in the trailers was really a slumming thespian named Trevor Slattery incensed many fans. The 'real' Mandarin was later revealed to be Guy Pearce's Aldrich Killian... or so we all thought.

Perhaps in an effort to appease disappointed fans, the studio shot a semi-canonical one-shot Long Live The King. The short demonstrated that the 10 Rings lived on in the wake of Killian's demise and that the real real Mandarin is still out there somewhere. Unfortunately, we'll probably never know who he (or she) is.

18 NATHAN FILLION IS WONDER MAN

This tease came not from one of the Guardians Of The Galaxy films proper, but from director James Gunn. In a scene that didn't make the final cut of the movie, a theater was shown playing a 'Simon Williams Film Festival'. The actor Simon Williams is known to Marvel fans as the alter ego of the hero Wonder Man and was played by none other than Nathan Fillion.

We can't rule out the possibility that the beloved actor will ever step into the familiar black and red suit, but it certainly seems unlikely. Heck, we'd even take the trailers for these Simon Williams films as special features on a Blu-ray release some day.

17 HEROES FOR HIRE

Iron Fist Luke Cage Defenders

Who doesn't love a good double act, and Luke Cage and Iron Fist represent one of the best that the Marvel Universe has to offer. The two share a dynamic that many great comic book double acts share from Green Lantern and Green Arrow to Booster Gold and Blue Beetle. They're exactly the same... yet they're totally different.

We saw the beginnings of the friendship between the two in The Defenders and Season 2 of Luke Cage. However, corporate changes at Disney and Marvel television appear to spell the end for the relationship with Netflix. Both Iron Fist and Luke Cage have been canceled and neither Marvel nor Netflix seems to have any desire to give the Heroes For Hire their own show.

16 THE WATCHERS

Watchers Guardians of the Galaxy 2

In one of several post-credits sequences for Guardians Of The Galaxy Vol. 2 we got our first look at The Watchers. These celestial super-beings are among the most infinitely powerful in the Marvel Universe. They are practically omnipotent; able to remake the fabric of the universe to whatever end they choose. Fortunately for us, most of the time they are content to observe us from afar.

We would expect beings of such enormous power to play a greater part in future films but they were notable by their absence throughout the events of Infinity War. Perhaps they will show their hand in Avengers 4? If anything will get them down from their ivory tower, it's the decimation of 50% of life in the universe.

15 ABOMINATION'S FATE

Abomination

The Incredible Hulk is quite probably the most underrated and underappreciated film in the entire MCU canon. Nonetheless, the film's comparatively poor box office performance coupled with Universal's distinct unwillingness to permit Marvel Studios to make another solo Hulk film mean that we'll probably never see a sequel.

There were many questions left unanswered by the film and teases dropped to set up future sequels. One thread left dangling was the fate of Emil Blonsky, aka The Abomination. Did he survive his encounter with The Hulk? If so, what prison could possibly contain him. While the Marvel one-shot The Consultant teased that Blonsky was still alive and could even play a part in the Avengers Initiative, this dangling plot thread was never revisited.

14 MILES MORALES

Donald Glover Spider-Man Homecoming

Donald Glover is always a treat to watch. But aside from his witty and amiable performance in  Spider-Man: Homecoming, veteran Marvel zombies got something even more special from  his presence in the film. The character Glover plays is called Aaron Davis, known to Marvel comics fans as the Ultimate Universe version of the villain Prowler.

The character is famously the uncle of Ultimate Spider-Man Miles Morales. In fact, he even briefly mentions having a nephew in the scene he shares with Spidey. It was a cool tease that led fans to believe that maybe they'd get their first glimpse of a young Miles in this film. Unfortunately, however, the tease ended up being nothing more than a cute easter egg.

13 THE PRESENCE OF ATLANTIS / NAMOR

Iron Man 2 Namor Tease

This one was a real 'blink and you'll miss it' kind of moment, but one that set the hearts of Marvel fans around the world aflutter. In the penultimate scene of Iron Man 2 as Nick Fury and Tony Stark converse, a S.H.I.E.L.D map can be seen in the background. On this map are featured many sites of strategic interest to the peacekeeping organization.

Wakanda is on there, as is the site where Mjolnir landed in New Mexico. But most intriguing of all is a spot off the Eastern coast of Brazil. This was later revealed to be not the city of Atlantis but Namor's personal fortress. Given the rights debacle in which Namor is entangled, who knows if this will ever pay off?

12 THE INHUMANS' THANOS TEASE

Inhumans

It's both a tragedy and a travesty that a property so ripe with storytelling potential as The Inhumans was treated so poorly. Despite its grand theatrical IMAX release, the series looked cheap and rushed while neither the plot nor the formal elements were becoming of the standard we expect from Marvel.

The one flicker of promise the show held was in the season (and presumably series) finale. Here, Black Bolt asserts that relocating from their base on Attilan to Earth will make them vulnerable to a coming threat. Fans assumed that this was a reference to Thanos, and this gave us the barest glimmer of hope that the Inhumans may face The Mad Titan. Alas, it was not meant to be.

11 THOR AND VALKYRIE'S RELATIONSHIP

Whether you cared for the tonal shift or not, it's hard to argue that Thor: Ragnarok didn't breathe new life into the Thor franchise. Among the film's many highlights was the ever-intriguing Tessa Thompson's portrayal of Valkyrie, an Asgardian warrior turned hard drinking people trafficker.

Thompson and Chris Hemsworth enjoyed great onscreen chemistry together and the narrative hinted that their relationship might develop further into an unlikely friendship or even a romance. Curiously, however, she was altogether absent from Infinity War. While director Joe Russo confirmed that she has survived the infamous snap, it is unclear whether she will fight by Thor's side in Avengers 4.

10 THOR'S VISION

Hey, remember in Avengers: Age Of Ultron how we stopped everything just to watch Thor take a bath? While Chris Hemsworth's impressive physique is always a sight worth beholding, the entire plot thread that saw him bathe in the waters of the Norns' cave never lived up to the scene's ominous tone.

Sure, the scene made Thor aware of the Infinity Stones, but there were other elements of Thor's vision that never quite paid off. Heimdall's warning that Thor would bring about the destruction of Asgard and all its people, for example. Perhaps this pre-empted Thor's tricking Surtur into destroying Asgard while he saved its people in Thor: Ragnarok but the disparity in tone suggests that was not the original plan.

9 DOC SAMSON

Doc Samson in The Incredible Hulk

Doctor Leonard Samson is one of The Hulk's most recognizable supporting characters. However, his role in The Incredible Hulk was fairly limited. Infuriatingly the character, played by Modern Family's Ty Burrell, actually had some great scenes with Edward Norton's Bruce Banner which are available on the disc but were cut out of the film.

We're not saying that we wanted to see Burrell don a long, green wig and leap into action at the Jade Giant's side but... actually, scratch that. That's exactly what we wanted! Suffice to say, Doc Samson is one of many elements of Hulk's mythology that has been abandoned by the MCU.

8 LUKE CAGE: KINGPIN OF HARLEM

luke cage finale

Opinion seems divided on the second season of Luke Cage, but most agree that it left us on an interesting cliffhanger. After being left his deceased nemesis' club Harlem's paradise, Luke Cage appears to essentially declare himself the Wilson Fisk of Harlem. Comics fans will remember when Matt Murdock pulled this exact same trick in Daredevil #50.

After an epic brawl with Wilson Fisk Murdock declared that if Hell's Kitchen needed a Kingpin so bad, he would step into that role. Cage seems to have done the same thing here, an unexpected move that was rich in dramatic potential going forward. Sadly, since the show has now been cancelled, we'll never know what happened next.

7 THE FAMILY TIES OF THE GRANDMASTER AND THE COLLECTOR

The Grandmaster The Collector

When Jeff Goldblum was cast as The Grandmaster in Thor:Ragnarok it was a huge tease for dedicated Marvel fans. Not only did it mean that we'd get to see Goldblum's inevitably enjoyable turn as one of the Elders Of The Universe, it meant that we might some day get to see him share scenes with Benicio Del Toro's Collector.

In the comics, the two are brothers and the idea of seeing these two acting powerhouses share a screen together in a Marvel movie was an extremely exciting prospect. Unfortunately, The Collector did not appear in Thor: Ragnarok and (presumably-we never actually see it) met his possible end at the hands of Thanos in Infinity War... oh well.

6 ADAM WARLOCK

Guardians of the Galaxy Vol. 2 Adam Warlock

In Guardians Of The Galaxy Vol. 2 we met The Sovereign -- a powerful alien race who are not born but genetically engineered to maintain the genetic perfection that they believe themselves to have attained. The Guardians find themselves at odds with the alien race and pursued by them across the galaxy.

The film's fourth post credits scene we see their High Priestess Ayesha's final act of revenge, birthing pod containing an extra special creation. Ayesha names this gestating creature Adam, a clear nod to Adam Warlock. Warlock is a cosmic hero of almost Godlike power and firm fan favorite character. Unfortunately, with the status of GoTG 3 up in the air, we may never get to see his adult form.

5 DONALD BLAKE

Thor Donald Blake ID

Marvel fans who only know Thor through his appearances in the MCU could be forgiven for shrugging when he briefly assumes the identity of Jane Foster's ex Donald Blake. Fans of the comic, however, know that for many years Blake was essentially Thor's alter ego; a conduit through which Thor could travel to Midgard.

After the bifrost was destroyed in the original Thor, many fans theorized that the unwitting Donald Blake would be instrumental in somehow facilitating Thor's return to Earth. Fans of Mr. Blake would be disappointed, however, as the good doctor was never seen or even referenced again in the MCU.

4 STEVE ROGERS AND SHARON CARTER'S RELATIONSHIP

Captain America Civil War Sharon Carter Steve Rogers

It's hard to imagine that there was a time when we were unsure whether Captain America could work for a modern audience. Perhaps in the hands of a lesser actor, Cap might not be quite so beloved today. Fortunately Chris Evans brought the exact qualities necessary to bring Steve Rogers to life.

We have spent the past seven years investing emotionally in Steve Rogers. Tragically, however, it seems that we may never see him happy and content in love. While we saw the beginnings of a romance with Sharon Carter in Civil War the relationship remains in limbo. Since Evans has hinted that Avengers 4 will be his last turn in the red, white and blue we may never see Steve get a long-belated date.

3 PHIL COULSON'S RETURN

Agent-Coulson-MCU

While we will see Phil Coulson return to the big screen in '90s-set Captain Marvel next year, it seems unlikely that we will see him reunited with The Avengers in Avengers 4. Ever since Coulson gave his life to subdue Loki in The Avengers before being resurrected in Agents Of S.H.I.E.L.D fans have wondered whether they would see Coulson return to the Marvel movies.

Since Coulson appears to have sacrificed his life in the Season 5 finale of Agents Of S.H.I.E.L.D (and we really don't think he'd be cool with being brought back again) we will sadly never see him reunited with the likes of Captain America, Iron Man and Thor.

2 THE O.G. GUARDIANS OF THE GALAXY

Even among comic book readers Guardians Of The Galaxy was a fairly obscure title prior to 2014. Those who only know the Guardians from the movies may be surprised to learn that Star-Lord's crew were not the first iteration of the intergalactic band of misfits. Indeed, it's even hinted that Yondu and his band of Ravagers were the original Guardians in all but name.

Guardians Of The Galaxy Vol. 2's second post credits sequence implied that in the wake of Yondu's demise the O.G Guardians were getting the band back together. Since the third movie has been put on indefinite hold we may unfortunately never see this motley (and phenomenally well cast) crew return to the big screen.

1 THE LEADER

Samuels Sterns

All of the MCU movies are jam packed with Easter eggs to tease eagle-eyed fans and The Incredible Hulk is no exception. Unfortunately, its combination of less than stellar box office performance and a difficult relationship with Universal relegated the underrated film to a dark, dusty corner of the Marvel film canon.

Perhaps the most egregious abandoned tease was the shot that saw Tim Blake Nelson's Dr. Samuel Sterns start to undergo an intriguing metamorphosis. After coming into contact with Bruce Banner's blood, Sterns' head starts to grow and undulate. This is a clear tease that Sterns is destined to become the super intelligent villain The Leader... sadly after a decade, this epic tease was never revisited.