Editor’s note: This post contains spoilers for the first issue of “Dark Nights: Metal.”

When Scott Snyder began plotting the first issue of DC Comics’ “Dark Nights: Metal” more than a year ago, he had a dream scenario. He just wasn’t sure he’d be able to make it happen.

At that time, Snyder already knew that the six-issue monthly miniseries would feature a who’s who of classic DC Comics characters, many of whom Snyder had never written before. Readers would be taking a journey into the Dark Multiverse, a previously unheard of area of DC continuity where nightmares and reality collide, featuring multiple evil versions of heroes such as Batman. Nth metal, an element familiar to the world of Hawkman and Hawkgirl, would also play a key role.

There would be lots of lasers, dinosaurs and Justice League action, as well as the highly anticipated reunion of Snyder and artist Greg Capullo; the two collaborated for a five-year run on DC’s flagship “Batman” series, catapulting both to big-name status in comics.

Snyder previously told The Washington Post’s Comic Riffs that “Dark Nights: Metal,” which will debut Wednesday, would be a thank you to fans of DC Comics who stuck with the publisher through the ups and downs of its 2011 “New 52″ reboot as well as the success of the current “Rebirth” era. As special as “Metal” was shaping up to be, Snyder was aiming to make the story unforgettable.

That was the moment he decided to reach out to writer and comic-book legend Neil Gaiman.

Snyder was preparing to take DC’s heroes to a place they’d never been before, and there was a character in Gaiman’s classic Vertigo Comics series, “The Sandman,” that Snyder thought would be the perfect guide into the unknown: Dream. So Snyder asked Gaiman for his permission to use Dream in “Dark Nights: Metal.”

To his surprise, Gaiman liked the idea. After exchanging emails about Dream’s role in the story and the many surprises the character would explain, Gaiman told Snyder words he won’t soon forget: “I love it. Go for it.”

“I was so excited. It was one of the greatest days of my professional life,” Snyder told The Post. “[Gaiman] couldn’t have been more generous. I just want to say thank you to him for sharing such an incredibly special character with us. It’s literally one of the best moments of my career, to be able to get to write a character that meant so much to me growing up and still does.”

Dream appears on the final page of the first issue of “Metal,” alongside Batman. Snyder says the character’s role in the story is “crucial.”

“[Dream] has some very key moments that spin the story in its essential directions,” he said. “At the same time, this really is a Justice League story focused on their discovery of the Dark Multiverse and the invasion with these evil Batmen [now] here and the desperate attempt to stop that using Nth metal.”

As big of a shock as Dream’s involvement may be to some fans, Capullo, who jokes that his most difficult challenge in illustrating this story is “surviving it,” says there are even more major moments in store.

“This [story] keeps going crazier and crazier,” he said. “You haven’t seen anything yet.”

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