Creating a ghost is a really simple task. You can create two types of ghosts: the mortal ones, and the immortal ones.
The first type of ghosts are those ghosts that the player can kill just by fighting them. The immportal ghosts, however, are attached to a cursed pile of bones that needs to be destroyed before the player can hurt them.
Let’s start by creating a ghost. Select Npc/NpcGhost and right click anywhere to place the ghost. At this point the level is already playable and you could just click on Save changes and then on Play to fight the ghost. This ghost can be defeated just as any other enemy, casting spells on it. But now let’s create an immortal ghost.
Select Npc/NpcCursedSkeleton and right click to place it near the ghost. Note that this cursed skeleton will make the ghost invulnerable until the cursed skeleton is destroyed. If you want to have more than just one immortal ghost, then create several cursed skeletons, one for each ghost.
When the game starts, the game assigns each ghost to its nearest cursed skeleton. It’s that simple, you don’t have to do anything else, just place your ghosts, place your cursed bones and then play the map. That’s it! Now you can save the map, play it and see how the ghost can’t be hurt until the cursed bones are destroyed.