Ghoulfriends 'til the End by Gitty Daneshvari

The ghoulfriends' new GFF, Wydowna Spider, starts to clear the cobwebs about the mysterious threat to Monster High. The previous generation of monsters formed a secret society that seems bent on turning the school into something that's more like a prison! But when Rochelle Goyle, Robecca Steam, and Venus McFlytrap uncover a second ancient group of monsters...the fate of the student disembody is in their hands!
 
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