I saw new encounters for Ghost, Naga, and Brigand. Aced them all. Though had no alcohol for Brigand. That's what I saw in my first go through of the area. (1rst character, got number 1 hero already, ironman mode.)
As for some suggestions to build up the 3rd area:
Obviously add the stronger encounters for Knight and Jester in there. (Have Knight disappear from map 2 and show on 3. Jester will be in a more fight-y mood.)
You might already have some plans for Volcano Lady being somewhat already warmed up.
Have you tried thinking up a Gargoyle? (Volcano area golem?)
Actually be able to fight "Horrible Presence" in third area. Maybe?... (final guardian of Demon King?)
Gadgeteer won't be too friendly anymore if you see her there.
Actual Succubus and Incubus demons. (Obvious reasons.)
And obviously there's gonna be the Demon King Castle at the end. Right?
Also just thought of this, Perhaps tie some of the endings with unlocking new Races for our Hero? Centaur, Ogre, Spidoo, Goblin, Demon.