What did you affect?

Text posts that have links somewhere in them, like how you'd add a link at the end hoping it would use that as the thumbnail. It was an SSL compatibility issues, so some sites it just would never work for.

I made a GIF banner, but could only upload JPG and PNG

That sounds like a good feature, adding gif support. I imagine they had some sort of reason for not doing it, but it beats me. Wtf they have an animated png it looks like: https://saidit.net/media/OihIEnKVVHzElZZTyGAyo-VRsOdUMMkY-sNauKDLT_c.png I don't know what kind of black magic this is.

I'd like to add multiple lines with links. Currently I can only do one line and it seems "inert" (I can't select it).

Yeah CSS hacks are a pain. I'm not sure how to pull that particular one off. The old IP2 theme had some links across the top we could have copied. Why not add that stuff to the sidebar description field instead? Maybe we could find an example on reddit.

Yes, let's do the mobile themes. You do them from your normal computer on a mobile simulator. Fancy shit. you just gotta find the button:

https://developer.mozilla.org/en-US/docs/Tools/Responsive_Design_Mode

https://www.sitepoint.com/how-to-simulate-mobile-devices-with-device-mode-in-chrome/