Alzrius,
I did some digging, and found a file listing all of my professional credits on my hard drive. The article appeared in Polyhedron #135.
Blackdirge: Take a look at Armies of the Abyss, which I wrote for Green Ronin, specifically the short section on "other" demons (I'd give a page number, but would you believe I've given all of my copies of Armies of the Abyss away?). To make a long story short, the demons I hinted at in those sections are the ones that seem to be proprietary to D&D. Off the top of my head, that's Graz'zt, Lolth, Yeenoghu, Fraz'urb-luu, Demogorgon (the name is public domain, the details are not) and maybe one or two others. Kostchtchie is from Russian mythology.
Arcane Runes: I probably wouldn't print anything longer than 5,000 words, which in the case of the elemental princes of evil might mean using Dungeon-style stat blocks rather than the more spacious Monster Manual approach. I might go up to 7,000 if the pitch was really good.
I'm glad people seem to be liking the Pazuzu article. THIS is the type of Dragon I'd like to publish. There will be much, much more.
The Far Realm is only a month away.
--Erik Mona
Editor-in-Chief
Dragon & Dungeon