Henry,
I read the books but I never quite believed they did that in 2nd edition. (Though I did face off against a Death Knight at 30th level...Killed half the party and the rest...well barely fended it off.) But not surprised they were death incarnate in 1st edition.
Again have to recheck to see how they did that in DLCS.
Pants,
Yeah
but the humaniod type one almost crushes any competition, especially in a Zone of Descration.
But I do agree, Soth will probably be based on the DCLS as it's more in keeping with his power, plus the fact it's Dragonlance. My guess for his class levels, (on the non-skirmish side), Knight of the Rose 10/Blackguard10/Fighter5.
He's certainly CR 25, as he's on par with Kazgoth in terms of power and prestige.