I know whats chasing the Vasari. It's Frogboy.

you could actually get karma for this..

It's a virus like culture that's chasing the Vasris. Do you guys remember the beast in homeworld cataclysm? It's similar to that and it spread through matter and anti matter. It was released by an unknown race that were so advance that they themselves had contained their own faith. Eventually triggered by an opened like minded Vasari scientist race experimenting, thus discovering on what should not have been discovered. This could be a force that no one has ever encountered. An advanced race that had evolved on a higher plane of consciousness but so much immature that their mind are set to conquering anything on their way.

Thank you for making some sense, Turchany.

I've read about these three theories before, but I'd rather have it confirmed than just be...theories, y'know?

I wouldn't doubt it.

I don't think anyone will ever know.  It's just a part of the storyline.  Theories are theories, and until we get confirmation from someone, that's the way it'll stay.  I don't know how many threads have been created with pretty much the same title.

*SQUEAL* He's not dead!

I IS YOUR BIGGEST FANBOI FOREVERS MECHA!

It's the soap that's chasing the Vasari... the SOAP!!!!!!

Two polar bears are sitting in a bath tub...

The first polar bear say to the second "Can you pass the soap?"

The second polar bear says "Soap?  No, Radio!"

Maybe there was no enemy after all, but that their universe is desyncing and minidumping.  Those who were caught in the tsunami of glitches were driven mad before becoming part of it.

While the idea of the Universe ripping at it's seams is indeed interesting, it would be a disappointment.

Every new expansion mentions the THREAT that approaches and the Vasari are clearly increasingly desperate, specially in Rebellion where the intro narrator even sounds worried as he muses if the warnings are true...

That the Vasari are now considering to even take humanity along, and the very real fact that this war has been going on for decades, while the pursuer keeps approaching, it makes me feel their arrival is nigh.

All this makes me believe we will soon see this threat and that we will fight it, so I would rather get something I can fight, I cannot shoot a universe that's going BSoD.

Maybe the Phase Demons idea? It does sound creepy enough.

IT IS ME.

Dylan Hunt and Tear Anasazi. 

What if it was just one pursuer?  A lab experiment gone awry?  An ultimately powerful physic being, able to destroy planets and control trillions of people with ease?  A nearly immortal vengeful creation, bent on destroying all Vasari, and freeing their slaves, traveling with the mind-controlled Dark Fleet?  The living embodiment of dominance, a billion times more powerful than all the Advent combined?  Coming this way? 

Phase Demons sound fairly explainable.  I mean all the races have been tearing the fabric of space and invading another dimension all in the name of progress...

That's my favorite explanation too, sadly most people want it to me nanobots for some reason.