Can we clarify the current lore for Preternia?
The Three Towers were there. Lady Slither had the Snake Lair as a base.
In Origins He-Ro's minicomic, when he was young, the Great Black Wizard was around with a base called the Ebon Fortress, and Rattlor and Tung Lashor were seen working for him instead of King Hiss or Lady Slither.

So what's the deal with Preternia? Who lived there?
In Origins He-Ro's mini-comic, we see He-Ro, Eldor, Moss Man, the Great Black Wizard, Rattlor, Tung Lashor and Draego-Man. We also know Sharella and He-Ro were adoptive family who fought together.