Thing 1: I changed the wiki logo, but as soon as JavaScript gets loaded, the logo changes to the old (glitched) one. Any fix? I'm not sure what the problem is.
Thing 2: I want the domain changed to "greatcharacters.miraheze.org". Keep "greatcharacterswiki.miraheze.org" as a redirect to the new domain.
@MarioMario456 Standard practice for wiki database renames is not to include a redirect from the old, prior database name, as that would prevent other wikis from requesting that database name, and it's a bit problematic to try and follow up to remove the old redirect in a month or two. Would you still like to proceed with a rename of greatcharacterswikiwiki to greatcharacterswiki? Personally, my best advice would be to keep greatcharacterswikiwiki and instead request a either a free custom domain from Freenom here or request a custom domain on a Qualitipedia domain. Now that I think about it, I believe the latter is the plan for the Qualitipedia wikis, so I'd just suggest that instead, as then your Miraheze subdomain will not matter as it will just redirect to the custom domain.
Regarding #1, can you clarify this a bit? This seems like it's either a recent logo change, which can take a few days to be fully updated, or it's an issue with your wiki's JavaScript. If the former, I'd suggest waiting a few days. If the latter, I'd suggest investigating your wiki's JavaScript code.
When I fixed the wiki logo, it took a while to update itself, but also for a while, JavaScript then replaced the wiki logo. It fixed itself (as I said).
About the database rename, do not leave a redirect. I'll announce that the domain will change via sitenotice.