I was curious as to how to work a Ghost's Malevolence ability upon an Eidolon. If the Eidolon is dismissed does the ghost continue possessing the Eidolon and thus back to the material plane when summoned again or does the Eidolon leave the ghost behind in his former space? The main text that gives me worry is in the text of malevolence it states "the ghost can merge its body with a creature on the Material Plane".
I'd say either it prevents the eidolon from departing or it hops along the magical eidolon link and takes over the summoner.