Giles using the revealing spell on Hans and Gretta.
This spell was used to force a demon to reveal its true form. It was used on a demon using the guise of Hans and Gretta Strauss. Whether or not the spell is exclusive to the demon or could be used on any other being is unknown.
Unlike most spells, the revealing spell had Germanic origins. The spell required the German incantation and a potion of unknown contents and ingredients.
The demon forced to reveal its true form.
The potion was thrown and smashed at the feet of the children guise, forcing them to embrace and morph together into the true form of the demon.