Onderon is a vibrant world full of all sorts of non-humanoid life and bestiary. What little civilization that lives on the planet's only (civilized) city of Iziz keeps a watchful eye over their walls. The planet's nearby moon Dxun, also known as "the Demon Moon" is inhabited by descendants of ancient Mandalorians. They too keep the watch, but over the ancient tomb of Freedon Nadd, a once-powerful Sith Lord.
Sorry but you are not allowed to view spoiler contents.
Dxun is also home to Sisterhood of Imperial Sith. Its founder, Darth Hera, was once an apprentice-turned-lover of Palpatine. As her power grew, she could not bring herself to obey the Rule of Two and thus lacked the will to fight Palpatine (as to replace him and take on an apprentice of her own). On one fateful day, Palpatine sensed this weakness and confronted Hera and forced her to fight him. After besting Palpatine in a lightsaber duel, Hera chose to exile herself because she foresaw Palpatine's rise to power and how his destiny was far greater than her own. During the Imperial Era, Darth Hera founded the SIS as a "contingency" in case Palpatine met his demise, or in the event that he needed to be killed. She took on a number of apprentices, four of whom became her High Council: Jana Sable, Katoh Niyne, Minajj Ventress, and Zekina Talon. Over the years, their numbers swelled and now several dozen Sith Ladies proudly call themselves "Sisters."
(https://docs.google.com/drawings/d/e/2PACX-1vTtho3r-0UGLf4fR81IsErnRVlK3tM2qk3tkfTJZvX-DNtLkwQYZqwBV44DMxGhfYDkS-sxaAzkIo28/pub?w=899&h=345)