The world of Harry Potter comes alive with this I Solemnly Swear...Mischief Managed Transforming Thermal Mug. Fill this magical mug with hot liquid and the text transforms from I Solemnly Swear That I Am Up To No Good to Mischief Managed. In addition, the 11-ounce mug also also turns from black to white, completing the transformation. A WBshop.com online exclusive! Not microwave safe, not dishwasher safe. Please note that this mug will come with a protective, removable clear film.