Collective Nouns for Various Monsters

Sirens: harmony

“The harmony of sirens gazed hungrily at the approaching ship.”

Mermaid: Splash

“The splash of mermaids harvested the moonlight, making pearls.”

 Candle: A group of corporeal undead.

“A candle of zombies descended upon the campers, devouring them.” 

Vapor: A group of non-corporeal undead.

“A vapor of ghosts came through the wall, terrorizing the wedding party.”

Mirror: A mixed group of corporeal and incorporeal undead.

“The necromancer guided a mirror of undead against the invading army, decimating their ranks and providing fodder for fresh recruits.”

Coffin: A group of vampires.

“The coffin of vampires attended to each others’ hair. Clip snip gel flip, marvelous!”