The Thesos Empire is a mysterious Empire, notable for having a homeworld that vanishes from the night sky, only to turn up in a slightly different place. As a result of this, some have theorized their homeworld, Zothea, to perhaps come from another universe.
These teleportation events mean that nobody knows the exact position of Zothea. the Thesos Empire is very hostile, so no research ships have ever managed to figure out any of their secrets. Those that survive report that the Thesos Empire has completely weaponized antimatter. If so, this could make them on the league of a Type-2 or Type-3 civilization in sheer power.
The Thesos Empire has much better technology than what they should currently have at their level of technology, which could mean that they are much more powerful than they seem. The Thesos empire may have entire galaxies under their command, without anyone else even knowing. some even say that they can go interdimensional. A feat only done by theroized Type-VII civilizations. This has not been proven, but if it is, it would trigger a mass exodus within our universe.
The Thesos Empire has been rumored to manipulate antimatter to their favor, as you have seen from earlier. Very low quality photos show that citizens of the Thesos Empire are very much powerful, and their military has weapons that can take almost limitless amounts of energy from other stars. Ships from the Thesos Empire have had no pictures taken from them, but descriptions have said that they are mounted with warp drives and wormhole drives that can take them up to 12,000 lightyears on its 'low' setting.