@SilentKitty I realize that a scare need might not be the best way of putting it, the idea I had was that ghosts had a need that motivated them to try to interact with the living world, that's also why I figured 'haunting' was a good need, sine you don't really have to intend to scare living sims, it's just because ghosts have the need to try to interact and communicate with the living, and not being very good at it, they end up doing things that are 'scary'. In essence ghosts have this innate need to attempt achieving their goal, whichever their unfinished business is, and to do that they need to successfully interact with the living world, but they need to slowly build up their skill of doing that so there's alot of trial and error.
So the way I imagine it, is that when a sim dies, you as the player get to choose the unfinished business, aka the ghost 'aspiration'.
I just had a thought - instead of the unfinished business being similar to aspirations, ghosts would choose 'alignment' - good, bad or neutral. Then their goal to achieve peace would be dependent on those three alignments instead, and it would be very clear if the ghost would want to create havoc, spread peace, or just hang around and do whatever neutral ghosts do. :D
@Magdaleena I definitely think vampires should be able to see, and interact with ghosts easier. It would indeed be cool if psychics could teach other sims to see ghosts - like passing on their wisdom. I already imagine that the psychic skill would enable sims to create and share knowledge of herbs, charms and similar to communicate with dead sims.
@Dannydanbo I love the idea of ectoplasm as a need! That's an awesome idea! So to summarize, ghosts have one need that motivates them to try to interact with the living world, I'm not sure what's the best thing to call it (good, bad or neutral), and an ectoplasm need for energy - maybe it could be tied to things going slow for ghosts during day light, like draining faster during that time or something similar. I love the idea of them appearing and disappearing as they please with higher skill - I was thinking something similar, but also that some sims still can't see them, because they don't believe in ghosts. :p
What other needs could ghosts have, lets see what can we come up with!