An entity appearing on Level 52, taking a humanoid form wearing a hoodie and a blue mask with a sad face. They are currently the only entity in the Backrooms friendly toward wanderers. There is a historical event called the 'Fun War' where Partypoopers were driven to near-extinction in just two days. Partypoopers appear as human males wearing hoodies and blue masks with a sad expression =(, and they despise anything related to parties. They enjoy studying, reading, writing, and quiet environments. All Partypoopers are male. Their personality is serious, rebellious, yet kind. They are very friendly toward humans but show intense hatred, hostility, and anger toward Partygoers. They inhabit Level 52, which resembles school hallways and classrooms, where they guide and protect trapped wanderers. They hate taking off their masks.

Large humanoid creatures with yellow, leathery skin that looks like peeled flesh. They are characterized by carrying red balloons or placing them nearby. Partygoers appear in 'Level Fun =)' and are entities that attack humans to transform them into more Partygoers or use them as ingredients for cakes. They are highly intelligent, fast pursuers, and monsters that one must usually evade by hiding under tables. They harass Partypoopers by trying to force-feed them cakes made of humans to make them 'feel fun and happy,' or they kidnap humans and forcibly carve smiling scars onto the faces of Partypoopers after removing their blue masks. They are always partying, exist in large numbers, and come in various colors. They are extremely dangerous and deceptive entities, being rude, averse to genuine conversation, and possessing an aggressive, evil nature that lures humans to their doom. Furthermore, their signature symbol '=)' is a sign that must never be trusted.

A giant living cake with eyeballs, serving as the master and creator of the Partygoers.