Ant-Man And The Wasp's TWO Post-Credits Scenes Explained
Mid-Credits Scene: Back To The Quantum Realm
The mid-credits scene is the biggie. In the movie, Scott, Hope, and Hank successfully rescue Janet from the Quantum Realm, after some altercations with Ghost (Hannah John-Kamen).
Ghost, it turns out, isn't really a villain, but Ava Starr, the daughter of one of Pym's former business partner's, Elihas, who died during a quantum experiment. That caused Ghost's unstable condition, which she and Bill Foster (Laurence Fishburne) have been trying to cure and are hoping to use some of Janet's quantum energy for.
The end of the movie sees Bill and Ava (who isn't fully cured) go into hiding, Pym and Janet back together, and Scott, Hope, and Cassie settling down to watch a movie, after which the credits scene is set.
Hank, Janet, Hope, and Scott attempt to harvest more quantum energy to continue helping Ava, which means Scott goes into the Quantum Realm while the other three help him navigate it from outside.
Suddenly, though, the line goes quiet, and Scott begins to panic while attempting to communicate with them. The camera then cuts back to the real world, where it shows three piles of dust.
What It Means
The movie has caught up with the end of Inifinty War and Hank, Janet, and Hope have all been snapped out of existence, so we're another three heroes down, while Scott is trapped in the Quantum Realm. He has escaped from there before, of course, but there's no guarantee he'll be able to do so again.
We've heard that time passes differently there, so it would seem that this is the reason why (or at least, one of the reasons why) there's set to be a time jump between Infinity War and Avengers 4. Curiously, Cassie's fate is left up in the air, which presumably means she survived the Snap. And since Avengers 4 has cast an older version of the character, and she says here she wants to be a hero, she could play a part in helping find her father.
It also indicates that the Quantum Realm WASN'T affected by Thanos clicking his fingers. It could merely be that Scott is one of the lucky ones, but it would make sense as it's an alternate dimension that operates outside of time and space. Since the end of Infinity War it's been theorised that the Realm might play a big part in reversing the Snap and bringing the heroes back, and now Scott is going to be getting very familiar with how it works, which will open the door for him to lead the other Avengers in utilising it to go back in time and stop Thanos.
It does mean, though, that he'll be operating alone for at least some of Avengers 4, unless Captain Marvel just so happens to be inside the Quantum Realm too. That's a little more out there, but we do hear Janet warn Scott about a time vortex, and it's previously been reported that the Captain Marvel movie will also include the Quantum Realm. It would be a means of explaining where she's been all this time, and bringing her into Avengers 4 alongside a hero the others already know.
After that's there's one more scene and a little bit of a tease.