Walking through the alleys of the docks district of town, you hear an old, mad beggar calling out for alms. He claims to be a god, cast out from heaven and stripped of his powers. The party passes, tossing a few coppers to him. In thanking them, the madman refers to incidents in their childhood or distant past which would have been all but impossible for him to know.
What if casting magic changed (for a few hours or days depending on the strength of the spell) the colour of the skin of the spellcaster? It could lead sadly to a very racist world to rp in.