'Eternals' Introduces 3(!!!) Major Marvel Heroes in Its Credits Scenes
Make sure to stick around to the end!

This piece contains spoilers for Eternals, obviously.
Ever since Samuel L. Jackson cameoed after the credits rolled at the close of Iron Man, Marvel has turned its post- and often mid-credits scenes into something of an art form. Sometimes they're just for laughs, like the still hilarious shawarma gag at the end of The Avengers, and sometimes they tease more ominous things to come, like Thanos' spaceship showing up just when things in Thor: Ragnarok seemed fine and dandy. Weeks before the movie premiered, Marvel's Eternals took over the news cycle for its credits scenes, one of which surprised everyone by casting Dunkirk star (lol) Harry Styles as a character with major implications for the rest of the franchise. (The choice to cut the scenes when the film was screened for press when this information was bound to get out anyway as soon as it premiered is an interesting gambit and one that I am definitely not irritated by still.) Now that the movie's out, we finally know what happens in the credits scenes, which officially introduce three Marvel heroes into the new roster.
First off, a reminder about Eternals' cliffhanger ending: After saving the planet from cracking apart after birthing the giant Celestial Tiamut, the Eternals have split up, a few going off into space to search for more planets to save from the Celestials' genocidal reproduction program, and the rest stay on Earth to keep helping humanity out (one of whom, the child-sized Sprite, chooses to give up her powers completely and become human). Sersi (Gemma Chan) and her human boyfriend Dane Whitman (Kit Harington) are having a casual stroll litigating everything that's just happened, but right before Dane can tell Sersi a big secret he's been keeping from her, their Celestial overlord Arishem appears on the horizon and grabs Sersi and her fellow Earth-based compatriots Kingo (Kumail Nanjiani) and Phastos (Bryan Tyree Henry) and spirits them away so that their actions can be judged. Dane is left in shock, and the movie ends.
The first mid-credits scene picks up with the Eternals who went off into space—Thena (Angelina Jolie), Makkari (Lauren Ridloff), and Druig (Barry Keoghan)—sensing that something on Earth has gone amiss. Before they can act, Eros (Harry Styles) and his sidekick Pip the Troll (played by Patton Oswalt) teleport onto their ship and Eros explains that he knows how to help them get their friends back. In the comics, Eros is the brother of none other than Thanos, the Avengers' enemy throughout the first three Phases of these movies. Eros (also referred to by his superhero name Starfox) has Eternal-like powers, able to manipulate people's emotions, which often gets him in plenty of trouble. It sounds like Styles' appearance as Eros is more than a simple cameo, too, setting up a rescue mission for whenever the next time we see these characters turns out to be.
After that, the post-credits scene picks back up with poor abandoned Dane, nosing around a room full of artifacts until he opens a box with a menacing sword inside. He reaches out to touch the blade, which shimmers with some material that looks like those magnet shavings inside those little toys when you can give the cartoon guy a beard, which is absolutely what the VFX department was going for here, but before he can reach it, a voice asks: "Sure you're ready for that, Mr. Whitman?"
A couple things here: The sword Dane is reaching for is the Ebony Blade, wielded by his superhero alter ego Black Knight—which is probably what he was about to tell Sersi before she was snatched. The speaker offscreen is never revealed in the scene, but director Chloe Zhao revealed to Fandom that it is indeed Mahershala Ali's vampire hero Blade, whose own movie is coming up later next year. When Fandom asked Harington how he felt about that reveal, he said he had no idea it was even happening, so it doesn't look like Black Knight will show up in the Blade movie. (Then again, Marvel cast members lie all the time, so we'll see.) So, that's three major character reveals after their own movie was technically over. Pretty soon Marvel is going to start fitting entire movies into those credits scenes.