[Taqwus]

Succubi are nifty, but the lack of an armor slot hurts somewhat.

There's Belial, Lord of Corruption, IIRC, who has the 'corrupt commander' option; this presumably works on a broader audience than seduction. I believe I've corrupted Banes, for instance, Belial also can't wear armor (none of the Demon Lords can), but he's got quite a few more hp so it matters less. The Mictlan Lord of the Night gets all slots, but is a Mictlan-only pretender. *shrug*

The ethereal assassins would be Elludian Stalkers, IIRC; you can get them from either a random event, or if you find the high-astral site "The Hidden Kingdom of Elludia". They're rather ordinary aside from the intrinsic etherealness -- in terms of hp and armament, for instance.