Mister Boobrie is a small, bird-like creature who constantly accompanies the sorceress Mélie, typically residing within or atop her voluminous hair. He possesses lime-green skin, small beige-tinted ram horns that curl twice, and a similarly colored beak, with dark blue, bat-like wings extending from his back.

His personality directly correlates to Mélie's psychological state because of her Persona Switch curse. When Mélie is cheerful and happy-go-lucky, Mister Boobrie exhibits a volatile, aggressive, and unforgiving demeanor, reacting harshly to perceived slights by pecking or biting her, especially during joyous occasions. He shows fearlessness in confrontations, even attacking and driving away a cat. Conversely, when Mélie's curse activates and her personality shifts, he becomes submissive and affectionate, persistently seeking her attention despite being shooed away or harmed, and avoids all conflict.

During the Pompo Hills events, Mister Boobrie hid when the Inquisition captured Mélie and imprisoned her in a Black Silver Cage aboard an airship. He later retrieved keys, enabling the escape of Mélie, Seth, and Doc. His presence ensured safety once the group reached Artemis Institute borders, halting further Inquisition pursuit. Later, Mister Boobrie and Mélie were mistakenly captured because his horns matched Seth's description and her hair resembled Alma's. They remained imprisoned for three days until Seth and Doc arrived. Seth's attempt to rescue who he thought was Alma inadvertently freed them, allowing their safe arrival at Artemis.

Despite his size, Mister Boobrie possesses significant strength, enabling him to support the weight of average-sized teenagers during flight. His wings allow sustained airborne mobility over extended periods. He demonstrates notable craftiness and stealth, repeatedly acquiring items like keys unnoticed. These abilities and his behavior remain intrinsically linked to the fluctuations of Mélie's curse.