Mirror of the Gods
The nahualli utters a prayer to Tezcatlipoca and smears a mixture of his own blood (one point) and the blood of a sacrificial animal (anything the size of a cat suffices) across the surface of a mirror. The blood fades as it is smeared. For a number of hours equal to the caster's successes on his casting roll, the reflection of any person or item currently under the effects of a path or ritual (from any variety of blood magic, e it Thaumaturgy, Necromancy or others) glows softly when viewed in the mirror. If the mirror is made of obsidian, the ritual lasts an additional hour.
