When Action Comics was rebooted for the New 52 in 2011, All-Star Superman writer Grant Morrison took the reins for the first 19 issues (#1-18 and the prequel issue #0). Morrison's run was set in the early days of Superman's super-career, and established the character's origin story in the New 52 continuity.The run consisted of three main story arcs, with a few single-issue stories scattered among them. In the first story arc, Superman defeats his first major alien menace and learns about his Kryptonian heritage. In the second story arc, he faces the metahuman Captain Comet and angsts about the potential danger he's putting his friends in just by associating with them. In the one-shot stories, a group of supervillains travel from the future to kill Superman while he's relatively young and defenseless, and a group of heroes (including the Superman from the New 52's present day) travel back to stop them; a superpowered menace moves between alternate universes battling the Superman in each; a boy's life is changed when he "borrows" Superman's cape; and, in a Halloween issue, Superman is troubled by ghosts that are actually the prisoners of Krypton's Phantom Zone.The final story arc of the run draws together elements from all the preceding stories into a complicated story about Superman's first encounter with one of his classic adversaries which is simultaneously that adversary's last encounter with Superman and a close-run battle against a new, more dangerous enemy with a grudge against them both.
Grant Morrison's run on Action Comics contains examples of:
Big Red Devil: Vyndkvx takes on this look during the final battle. Only with some extra faces.
Bittersweet Ending: Superman triumphs, but the Kents are still dead as a result of Vyndktvx's schemes and Clark will never know that he avenged them. He even forgoes his one magic wish that could've brought them back and instead used it to resurrect the murdered Mars colonists, because he made a promise that he'd protect them.
Bully Hunter: Superman is depicted this way, as he was back in the earliest issues of the original Action Comics.
The Cameo: Vardox and Super-Turtle get mentions when Mxyzptlk shows up. Apparently they were attacked by Vyndktvx as well.
Civvie Spandex: Superman's first costume is a T-shirt (with the S-symbol printed on it) and jeans, accessorized with a red cape (made out of the blanket he was wrapped in when the Kents found him).
Continuity Nod/Mythology Gag: The first few issues hark back to the first few issues of the original Action Comics, and reclaim some of the famous Early-Installment Weirdness: Superman can't fly yet, is a lot more concerned with ground-level (sorry) social justice issues like poverty and domestic violence, and Clark Kent is working at the Daily Star, not yet the Daily Planet.
Lex Luthor's initial appearance is more out-of-shape than normal, confirmed by Morrison to be a reference to the notable rotund Golden Age Alexei Luthor.
Gsptlnz mentions Superman's contests with Mxyz, which for him haven't happened yet.
Disproportionate Retribution: Mr. Mxyzptlk is a 5th Dimension imp who works as the Court Jester for the land of Zrfff. He entertains the kingdom by annoying the heroes of several worlds, including Superman, and letting Zrfff watch. Enraged with jealously over Mxyzptlk's popularity and success, the kingdom's other jester, Vyndktvx, decided to uses his powers to secretly make Superman's life a living hell before eventually killing him, even assembling an "Anti-Superman Army" — and do it all before Superman ever met Mxyzptlk in the first place. Of course, Superman has no idea who he is, but Vyndktvx holds him responsible for Mxyzptlk's success because the kingdom really liked how he was the only hero to best Mxyzptlk.
E.T. Gave Us Wi-Fi: Almost literally. As revealed in issue 7, one of Brainiac's many identities throughout the worlds is Earth's Internet.
Fantastic Racism: An alternate reality version of Luthor is fighting against a black version of Superman. This Luthor is as white as his mainstream counterpart, and is adamant that he hates Superman as a fantastic racist, and not the normal kind. Simple mistake, he is a bald white guy known for his fanatical hatred of a black guy.
Ignored Epiphany: An alternate Lex Luthor realizes that Superdoom is the monstrous, egotistical bully of an alien that he always suspected his own Superman of being. However, he quickly goes back to wishing the BOTH of them dead after this brief moment of insight.
In a Single Bound: At the beginning of the run, as in the earliest Action Comics, Superman can leap tall buildings in a single bound, but not yet actually fly.
Innocuously Important Episode: Action Comics #9, sandwiched between "Superman Versus Brainiac" and "Superman Versus Captain Comet (While Batman Chuckles At His Secret Identity Problems)", was an interlude involving parallel universes, a Corrupt Corporate Executive who buys a machine of incredible power, and a black version of Superman who is the president of his America. The monster, Superdoom, comes to fight Superman in issues 17 and 18, at the behest of Vyndktvx.
It also establishes the new form of the Multiverse, which gets explored several years later by Multiversity.
Manipulative Bastard: Vyndktvx. It's even implied that he's the reason that Superman's character and life are so different from the norm.
Mistaken for Racist: In the alternate universe depicted in issue #9, where Superman is black, Lex Luthor (who is still a white guy) is shown arguing that he is not a racist and hates Superman because he's an alien, not because he's a black man.
Murder by Mistake: Vyndktvx's first attempt to kill Mxyzptlk instead resulted in the death of the king, who had swapped clothes with Mxyzptlk as part of one of Mxyzptlk's jokes.
The ending of the run reveals that Vyndktvx technically succeeded.
Mythology Gag: During Superman's battle with Captain Comet, he's trapped in a Lotus-Eater Machine daydream in which he's happily married to Lois Lane — which he quickly sees through because at this point in his history he and Lois barely know each other.
Oedipus Complex: Vyndktvx's hatred of Myxz is because he won the heart of Gsptlsnz, and the end of the story reveals she is both their mothers, due to the cyclical nature of the 5th Dimension.
Prequel: To the rest of the New 52, being set in the early days of Superman's career.
Trainstopping: In Action Comics #1, Lex Luthor causes a Metropolis bullet train to go out of control. Superman is able to stop it, but being as this is set in his early days, when he was weaker and couldn't even fly yet, stopping the train almost kills him, allowing Lex and the military to capture him. (Added Stealth Pun: Superman has to be faster and more powerful than a speeding bullet locomotive!)
Vicious Cycle: The rivalry between Mxyzptlk and Vyndktvx is actually a neverending 5D fable.