I'm currently trying to design a telepathic, mind-controlling alien species that resembles early theropods, like Dilophosaurus, or an abelisauridae, like Carnotaurus. My main concern is not the design, but the society. This society practically never invented anything besides giving the enslaved species ideas for them to make. What values they must carry, since they're nothing but very powerful moochers? How can they maintain the trust and authority over the enslaved species, especially as they are the ones who are thousand fold smarter?
Technological incompetence would be a late arriving trait in a telepathic/mind-controlling species, because prior to encountering another sapient species which they could enslave, they had to fend for themselves.
It could be, that due to limited intellectual potential, these creatures never evolved passed the hunter/gathering tribe level on their home world. They may have domesticated animals early due to their mind-control abilities, but not yet mastered tool-use or cultivation of food crops. Then a star ship arrived, containing their first batch of slaves.
If since then they have received no impetus to evolve beyond the tribal authority structure, then you might find them choosing leaders via mortal combat and a rigid pecking order, again enforced by combat. Strength however would be measured in the ability to dominate other minds. Blood combat, when present at all, would be handled by proxies. Or for an even creepier vibe, their blood combat could take the form of a game of blood and dust. One slave is thrown into an arena alone, with a knife and an hourglass. The challenger must make the slave commit suicide while the champion tries to stop him. If the slave survives till the hourglass runs out, the challenger looses.