Yes Nightmare does work well with GHEIST but so does Piranas.
Do you like Pill manipulation or other stuff? If you like Pill manip. use piranas, if you like other stuff (power manip. life manip.) use nightmare.
I'm reasonably poor, my favourite Gheist cards at the moment are astrid, dr saw, methane and arkn.
i really like to try different tactics in reguards to the manipulation question.
Been useing Bridget with them and with dr saw and astrid i really increase the life gap