In simplest terms, Prime is a sentient, anentropic universe. It is known that Prime eats other universes, though it goes to lengths to avoid consuming those with native sentience.
From the Mess, Prime is impossible to reach by conventional travel.
Prime creates science probes to explore the neighboring universes. These probes relay data to Prime that is in every way as accurate as possible to collect. Prime tends to create probes in the locations where they need to be if it is 'close enough' in spacetime to have influence in the target universe.
Those known to be connected to the Prime network are:
Those connected to Prime feel as though they are cooler than normal and may give off a faintly tingly sensation to the touch. Neural reactions inside of them will operate better than normal and their bodies generally seem to run more efficiently. Some will show certain psychological shifts (tending towards increased stability and reason).
Two other predatory universes have been specifically identified by name so far- Unity, which appears to desire the order inherent in universes, freezing them to preserve their order prior to their consumption, and Dissolving-Corruption, a universe described as completely ruthlessly expansionistic, currently locked in a 'war' with Prime. Prime is also aware of and has had conflicts with the Old, a race of multiuniversal 'gods', of whom Kelil is a representative.