Auzou Book about why a giant skeleton is very, very, very annoying

It's the day of the parents' visit to the mortal camp! There are plenty of werewolves, skeletons and autres barons voudous... but no grandma. Instead, she's sent someone who says she's my mother, but who looks a lot like Euphemia-who wants to destroy the camp to set up an amusement park, if you ask me... The camp isn't going to take this lying down, Leslie!