Originally Posted by Valloric
There's no WYSIWYG way to create tables in Sigil. In general, they're probably not going to work the way you want them with epub. There's the fact that the screens are small, and that the current Reading Systems don't handle them well.
You should honestly avoid them.
That's difficult to do for rpg books. There are just too many places where tables are essential tools for conveying a bunch of comparative information in relatively short space.