The new editor has absolutely no more BBCode support, as it seems. Clicking on Source gives me a single, long row of HTML text, which isn't really helpful. I need to copy over a topic from Retro that has a lot of stylization and stuff, and it's just annoying if I have to painstakingly insert those all again.
I used BBCode to set up my topic for Sonic Bash for Retro. Then with SSRG, instead of clicking on Source so it has HTML, just use it without it, and it seems to work. For example, I'm not in HTML mode and about to do (b)bold(/b), (u)(i)underline(/i)(/u) and (size=5)Size(/size) but replacing ( ) with [ ] ... bold, underline and Size If you're making a topic, and you want to preview the topic (seeming as I can't find the "preview post" button anymore), just click "Post new topic" BUT make sure your subject (or topic title) is empty. It will refresh with an error stating to insert a topic name, but will preview your post.
Eh, it's something, but half my text was still broken (I used more than just bolds and italics). Still, I'd wish there was a way to bring this old editor back.