You can make:
* Terrorgheist
* Zombie Dragon
* Abhorrant Ghoul King on Foot
* Abhorrant Ghoul King on Terrorgheist/Abhorrent Ghoul King on Zombie Dragon (he sits on top of it)
* Vampire Lord on Zombie Dragon (kit comes with the Vampire Lord parts too)
If you make the Ghoul King on foot, you can also make 1 Terrorgheist or Zombie Dragon. I've seen people do some weird creative bases like with the ghoul king on foot being removable from the base (to represent him "riding" the beast) but I don't think it's possible to make him removable if you actually want him on the beast (also be warned it's very flimsy positioning, like he is basically hanging on by his tiptoes usually) although I'm sure there's a way somehow, maybe with a small magnet directly glued to the rock on the base for the foot king, and where he kind of stands (on the Terrorghest the King is leaning forward, on the Zombie Dragon he looks more standing upright) on the beast, but I haven't tried it.