My concept of prankster comets in SFG:

The specifics of Daredevil Comets, Cosmic Comets and Purple Comets do not change.

Songs with prankster comets are no longer story mode songs (except Cosmic Battle) but variations of story mode songs OR freeplay songs.

Once a song with a prankster comet in orbit is beaten, the prankster comet song will appear in a special section named "Prankster Comets songs".

Prankster comets orbiting songs may disappear if another song is played in the meantime (like stars for Mario Galaxy), so you have to check often if there are any new prankster comets orbiting songs.

New prankster comet: the Fast Foe Comet. Greatly speeds up note speed.