Note: One thing is immediately obvious with this spell: the ingredients are relatively easy to come across, almost any desert and a general store will provide what one needs (assuming, of course, one has access to a magic wand and the store has the very seasonal toad spittle in stock). It would seem, therefore, that this spell is too good to be true, allowing one to move unnoticed amongst friend or foe, spy on lovers or would-be lovers, steam from the rich and give to the poor, or vice versa, sneak out of the castle for a midnight tryst, or anything else ones heated imagination might devise. Remember, therefore, one of the major nonmagical laws of the universe, "If it's too good to be true, it's too good to be true." This very powerful spell has two small drawbacks: it only works in a place where there is both fire and mist (and there aren't a lot of those around), and it only lasts for a short time. A very short time. Whatever one does after they cast it, they've got to be quick. The spellcaster's rule of thumb for this spell is contained in the following ancient verse:

How long is fast
How short is quick?
Enough to cast another spell
And make it stick

If one keeps the shortcomings in mind and knows when to use this spell, it can be of great use to its caster.