In Curse Of Strahd, Otto met the Pack, who convinced him that the Abbot had invited them as guests. When he found the Pack out exploring the Abbey, he was flustered, but ultimately let them wander the Abbey after his fellow guard Zygfrek Belview let them in.
Otto was a Mongrelfolk created by the The Abbot, residing in the Abbey of Saint Markovia. Like all other members of the Belview family, he lived a short and tortured life. Otto had patches of donkey flesh covering his body, as well as a donkey's tail, and also had a wolf's ear and snout with leonine legs. He was comparatively strong and fast for a mongrelfolk, however, and thus was given guard duty of the Abbey by The Abbot's right-hand man, Clovin Belview.
He believed he was the smartest, wisest, strongest, fastest, and most beautiful person in the world, but was jumpy, and could not process conflicting information easily. He was prone to whinnying and braying when made to make a decision, as though the process was physically painful, and was very wary of outsiders. To ensure that no one would challenge him, the mongrelman always carried a shovel with him, which he wielded in one hand like a battleaxe.