The Prize Ghost will appear haphazardly and rarely and has a bonus "prize" for defeating in Ghostbusters Beeline (Mobile app).
Prize ghosts appear haphazardly and very rarely. Defeat them to gain bonus cash or items upon the completion of the level. Prior to version 1.3.0 they would drop slime.
They will disperse from the level if not captured quickly enough.
Images provided by Adriana Munoz.