So what are The Horrors the Dunkelzahn is trying to keep back.
Shadowrun is the 6th World (or timeframe).
During the middle of the 4th Age, when Magic is at it's peak, astral spirits called Horrors are able to bridfge the gap between their innately magical home, and the Earth. It's like killing off the dinosaurs, and they set about torturing, killing and destroying about everything.
Towards the end of the 4th Age, magic starts receding, and they are weakened, some expiring on earth because they've stayed too long, others retreating home before the bridge collapses.
During the 5th Age, there's no magic.
Now, during the 6th Age, magic is ramping up again, and in a thousand years or so, that bridge will be reformed. Big D is going to hold that off for as long as possible.... you know, big Saving the World type stuff...
Also was it ever clear about why Chostwalker hates the Azzies so much? Aside from them being Azzies.
Ghostwalker has a particular hatred of Blood Magic, mainly because it attracts suffering (and Horrors). Most great dragons feel the same way, GW is just more assertive about it.
There's a quote from the old Earthdawn game (which is set in the 4th Age), where a great dragon is lamenting that Blood Magic is the greatest mistake dragons ever made (it may have even been GW in his former name. Mountainshadow I think?