Re: Regarding the Vasari enemy.
I don't know what it could be.... but I do believe the instruction booklets actually gave us an hint in a structure shared by all races:
Phase inhibitors stations.
The Advent? Copied the stations from the TEC after capturing some.
The first TEC Phase Inhibitors? Clearly stated to have been reverse engineered from captured Vasari Inhibitors.
And how did the Vasari create the Phase Inhibitors? Here's the catch explained in the booklet.
The Vasari simply "found" them around in space. Once they figured their uses, they did begin to repurpose them, but even they didn't fully understant how to manually replicate the technology so used their advanced nanite techs to just reproduces the stations as perfect copies of the original.
But still... they didn't create it. And nor did -any- of the two other races who only captured them from each others.
So whatever IS chasing the Vasari, I bet is linked to whoever -first- made the phase inhibitor technology in the first place.
Think about it: Whole systems, disapearing without a trace with almost, nay, with NO ONE making it back to say what happened, except a -single- ship whose crew was rendered mad with terror after the rest of their whole dark fleet similarly was defeated/disapeared. And a technology -purposely- made to -prevent- someone from properly leaving a gravity well(or at least, slowing down their attempt)... of which no one know who is the original creator.
Start to get my drift?
These inhibitors where already there when the Vasari found them, unperturbed relics of an ancient time, of a forgotten creator.
My guess is, whatever the Vasari did, maybe related to that Kron Vasari Lab in the original video "1000 years ago", is that it woke up whatever race made these things in the first places and got to stare at it. And it stared back as it decided to take it's rightful place again. Probably annihilating anything in it's site, Reapers like actually though not neccessarily living space ships of doom either.
Also, judging by descriptions of systems just "blipping out" and losing all communication, I assume if this enemy is ever made into a race it will also have major communication jamming technology, maybe as a major weapon of it's own. The kind of thing where when it attack one of your system, it suddenly jam -all- communication. Your units will still be there. They'll still be fighting, trying to do everything they can to survive... but you'll be unable to give them order. Or even to -see- what is happening as everything becomes "dark"... and as the race spread, you'll thus be only able to see more and more systems just purely "blipping out" on the sector map, which should just literally give an idea of what the Vasari dealt with.