-Thrall's changes: mor 18, weapon changed to quarterstaff, cost 0 gp, no longer recruitable but summoned;
-Thrall Berserker mor 18;
-New summoning spell (summons 20 Thralls);
-All leader vampires (even if made so by Gift of Reason) domsummon20 Vampires;
-Vampire heroes (except for Rage) summon Vampires as allies;
-Other changes I cant remember.
Added a fifth hero Red Cardinal (copied unique Belphegor[810]) that lowers dominion but automatically summons 5 Thralls (instead of Belphegors militia) and calls another new unit - the Red Monk. Belphegor is unaffected.
The spell "Create Thralls" obviously costs too much. Its not expected that a player will use it. It's there for a flavor and for AI summoning.
You could make it so it didn't cost too much though, couldn't you?
1) No one really uses thralls if they have a choice. Its just a flavor unit.
2) It wouldnt make too much sense if you got 20 Thralls from 5 slaves (I could explain it as a cloning ritual or something but it would feel forced).