HARRY POTTER Heat Changing Mug - Hogwarts Crest. Officially licensed merchandise. This Harry Potter mug is an absolute must-have for every fan of the world of witchcraft and wizardry. Cold, the mug shows the famous Hogwarts Crest featuring all four houses on a black background on the front, and the words 'Hogwarts School of Witchcraft and Wizardry' on the back. When hot liquid is poured in, the mug transforms to reveal Hogwarts School against a night sky, with several dorm room windows lit up from. A perfect gift for a true Harry Potter fan.