Yes, UDK have a base on UnrealScript. This language similar on Unreal 1 scripts. And yes, we are inherit classes from base classes, like this: We have a base class "Pawn" and we extended this class how "GhostPawn". It allows to do life easier.
Wonderful! So I assume you have already made your GhostPawns. I think the best base class for abilities will be Weapons. You don't want anything with a mesh (i.e. visible gun or whatever), so you can skip that. You can use the health of other pawns as the "fear indicator". Your ghost uses an ability (weapon), which inflicts a certain amount of damage and if the health of the mortal (pawn) reaches zero, he or she will run away/die/explode/whatever. For insanity you could use the Shield indicator. The Gold Plasm is a little bit trickier. If you use Weapons as a base for your abilities, you will need some kind of central ammunition supply that keeps feeding "ammo" into the "weapons" until the supply runs out and the game ends. Hmmm... Maybe you can use a modified Zone Actor (the same thing used for water and fire zones)? It can iterate through all weapons of a certain class and refill the ammo if it starts to drop (i.e. the weapon is being used). Yes, tricky stuff, but certainly doable. Do you already have some code or is this something you still need to build up from scratch?
I think that use of weapon is silly. Because we can't change one factor that pawn died after damage by weapon, but pawn must leave level. We have some code for now, I think that we shouldn't use weapons and health for Fear Indicator it won't stable and it fetch other problems
Hmmm... I don't quite agree. True, you can't stop a pawn from dying when its health reaches zero. But you can change the death sequence into anything you want! Back in the Unreal I days I programmed a Super Titan who walked over to the nearest enemy when his health ran out before blowing up.
In that case you can build a new class that immediately can control both Fear and Insanity. Although... Won't it in that case be better to not build a new class at all and instead include the Ability functionality in your Pawn? That makes things like Apparition slightly more manageable.