You've got the best of the best here and some of them I had to work hard to find!

I have trouble with the horizontal line sometimes too. The HTML commands are sometimes a bit less flaky than the markup coding.

The code for the horizontal line is <hr> (horizontal rule). <sup>text</sup> works to make text superscript which can be handy for making footnotes, eg. Footnote^{[Note 1]}. The carrot (^) is supposed to work in markup but again... flaky!