There are several ways to add subscripts and superscripts in Ulysses.

Use Special Characters

On Mac, the easiest method is to use the shortcut ⌘⌃Space (command-control-space) to open the Character Viewer. In the search field, type the character you need, for example, the number 2. Then, in the bottom-right corner, double-click the subscript or superscript version of the number to insert it at your cursor position:

Modify Markup Tags 

Alternatively, you can modify a markup tag on your Mac. In this example, we’ll adjust the export style so that anything tagged with the Marked tag :: in the editor will be superscript, and anything tagged with the Delete tag || will be subscript.

1. Go to the menu Ulysses › Settings… and switch to Styles.
2. Choose a style from the PDF/DOCX section, e.g., Swiss Knife.
3. Right-click on the stylesheet and select Duplicate.
4. Open the duplicated stylesheet in an editor of your choice, e.g., TextEdit or TextMate.
5. Look for the selector inline-mark and change it so that it looks like the line below:

inline-mark {
	baseline-shift: superscript;
}

Look for the selector inline-delete and change it so that it looks like the line below:

inline-delete {
	visibility:     visible
	baseline-shift: subscript
}

6. Save the stylesheet and rename it (optional).
7. Enclose the text in the editor with the Marked/Delete tag.
8. Select your customized export style in the export preview.

Please be aware that the tags will look different in the editor as they keep their original look as deleted and marked unless you change the editor theme. However, they will look as desired once the document is exported:

For your convenience, we have adapted an existing export style. It’s ready to use: Swiss Knife (Superscript, Subscript). Please note that you can only customize the export style on the Mac. However, it is synchronized to your iPhone or iPad via iCloud, and you can then select it in the export preview.

If you want to learn more about the customization of export styles, please check this informative guide.

Use Mathematical Equations

You can also use mathematical equations to write equations like E = mc² or CO₂.

The tag $$  will bring up an editor where you can enter equations. Use ^ for superscripts and _ for subscripts like this:

E = mc^2
CO_2

For more information on mathematical equations, please check this guide.