I have gotten to the point with mainstream American comics where I only really care about niche settings/characters that show up for a miniseries like once a decade and then disappear back into the ether until an author remembers they exist for some passion project or something.
Some of these are admittedly less niche than others, but, yeah
Amethyst, the Princess of Gemworld
showing up in a random issue of Green Lantern next month, and previously in a random issue of Superman last year and a Christmas story with Harley in 2023. She was part of Young Justice in 2019 and even had her own solo miniseries and graphic novel, but just faded away for whatever reason.
Currently showing up in a the Green Lantern Dark miniseries, which is being advertised as an Elseworlds story for some reason, and is over halfway done.
Most recent appearance prior to that was the Tangent Flash being a major character in the year and change long War World storyline in Superman in 2021/22
the New 52 version of Earth 2
Fuck knows when this lot are showing up again. Last appearance was Earth 2 Superman (Val Zod) and Red Tornado (Lois Lane) getting a side plot that was carried out over the course of two issues of Jon Kent in 2022, a Beast World event side issue in 2023, and then 2024's Black Power special.
Shade, the Changing Man/Girl/Woman
Currently getting backup stories in two issues of DC vs Vampires: World War V issues 10 & 11. Their first appearance since the last issue of Shade the Changing Woman in 2018, unless you count COPRA over at Image featuring a not-Shade-for-legal-reasons version of Rac as part of the title's totally not the Suicide Squad, but that just wrapped up its final issue this month, so...
Most recently a supporting character in Question: All Along the Watchtower, and I expect she'll show up in small roles in Justice League Unlimited and Batman here and there, but her last focus title where she was a main character was 2023's Outsiders where she was badly written and the series got cancelled early for being a bit of a mess. Prior to that it's been one-off pride stories here and there for the last few years or supporting roles in other peoples' books.
They actually just announced this last week that the original Starbrand will be a major character in September's new Battleworld miniseries, so that's neat.
Prior to that, Hickman had integrated a lot of the New Universe stuff into the main Marvel U in his Avengers run back in 2013 and the characters stuck around through 2016 or so before fading into obscurity again, afaik. I'm admittedly not as up to date on my info with this one, embarrassingly, so if I'm wrong please tell me so I can go hunt down some new books.
Currently featuring in the ongoing Imperial event from Hickman. First issue was a blast, very happy with it.
Prior to that was the Worldbreaker miniseries from Pak in 2022 that was only 5 issue but really wanted to be 12 and just ended up abruptly ending in an unsatisfying manner. Prior to that, characters popped up in 2021 and 2018, but the last appearance of the world itself was 2017's Return to Planet Hulk, acting as a soft-tie in to Thor Ragnarok.
Man, where the fuck is Miguel lol. Has been getting semi-regularly miniseries from Steve Orlando at a rate of one or year or so, and 2099 is a major locale in Marvel Rivals, and of course Miguel was in Spider-Verse in a major way. So I'm not actually too worried about this setting and characters getting put back in the box, but with Peter David's recent passing, I wouldn't be surprised if they rest them out of respect for a bit.
Gods only know what she's up to. Still mad about them randomly writing out her trans wife in 2018/19's Asgardians of the Galaxy title, and since then Angela herself has only popped up as a supporting character in Thor stories, and even then rather infrequently. Afaik, last time she was around was over a year ago in Immortal Thor. I wonder if she's quietly been set aside because of her association with Neil Gaimen and recent events.
Mojo's sometimes henchwoman. She basically never gets her own series, and any time she does manage to get extended regular appearances and actual character development, it all gets thrown in the bin the next time she gets used because authors don't give a fuck enough to know she's a real character who's moved beyond being Mojo's enforcer in the past 20 years.
Appears once a year or so, if I'm lucky. Last focus storyline was 2019's Mr & Mrs X where she fixed Rogue's powers for her, and before that was 2013's Uncanny X-Force volume 2.
MIA since February 2014. Not got much hope for more of her lol.