Ah, where to begin?
First appearance: Tierney Through the Looking Glass
If there is a BigBad in the Twingate world, there's a good chance that the Ta'bar'pur are it. So far they have only been seen in the alternate universe Tierney created in Tierney Through the Looking Glass, but it is possible that they will appear in this world.
The Ta'bar'pur spoke a language that may exist in this world as well, which would indicate that, well, they're coming.
They're evil. Or beyond evil, through evil and out the other side. They appear as utterly black figures swathed in shadow, their true forms hidden -- unless the shadows are their true form. In melee combat they are vicious and deadly, and they appear to have powerful arcane magic at their command. They are also just about totally immune to arcane magic, and strongly resistant to divine magic as well.
The only person ever known to kill a Ta'bar'pur is Salin, who got lucky and found an injured one and flame-struck the bejeezus out of it.
They fly great hulking black ships, and have the ability to transport large numbers of drones. These drones can take the form of humans, beholders, or mind flayers -- all have been seen drained of their souls and turned into mindless husks that serve the Ta'bar'pur. The Ta'bar'pur also use Iron Golems.
The Ta'bar'pur apparently entered the world through a game of chess that DukeEledin was playing with either a Ta'bar'pur leader or scout, or some representative. The AlternateReality was apparently caused by Tierney stealing a chesspiece from that board, which somehow changed the flow of time and caused the game to be decided in the Ta'bar'pur's favor.
There may be other methods by which the Ta'bar'pur can enter the world. Not enough is known at this time, although Dreams may provide a clue.
Once the Ta'bar'pur entered the world, they enslaved the immediate surroundings and set to work searching for specific magical items. At this time, no information about those specific items is available.
So, in short, we know one way that they can get here, but there are likely others. We don't know what they want, and we don't know how to stop them.
Enjoy.
-DMP