I'd also beware the advice given on solos from pretty much everyone. Don't make the fight just about the solo, give interesting features for the players to interact with.
Give coffins to hide behind or gain cover by.
Perhaps a font of water soaked through with radient power that can be used to soak the ghost once.
Perhaps give it a power where it starts to take a deep intake of "breath"/ or perhaps it starts gathering the shadows around it, giving the pcs a chance to run for cover, perhaps even inside a coffin, before it unleashes a wave of necrotic energy. "The ghostly form raises its arms and starts gathering the very shadows themselves from around the room, coalescing it into an orb as black as midnight that shudders as if the power can not be contained for long"
You could use coffins that churn out skeletal minions but can be turned off through locking the coffins or by destroying the gem inside, something for the controller and a striker or someone trained in thievery.
Make sure your bad guy has some means to free itself through the fight, either a rechargable teleport that takes a move action or a int vs will attack similar to the cleric cause fear, although i guess your aoe power may well do that, i guess you intend for it to be vs reflex?
The thing is to avoid turning it into a slugfest where they all stand round it and beat on it, movement and tactics make fights exciting.
