Going off the reservation

Just because a spell does not exist in the rule book does not mean it cannot exist. One of the best spells I ever used was in a campaign where the high powered characters had begun to trust their fortune tellers to predict major events for them. Just as an army was invading one of their allies, the invaders had their fortune tellers cast a powerful spell. As long as the spell was maintained, anyone trying to use fortune telling or a similar style of magic to see what was going on would get horrible images of an old crone instead of the information they sought. Card readers saw the crone’s face on their cards. Crystal ball readers saw evil eyes staring back at them out of the ball. Tea leaf readers saw the crone’s face form and then dissolve in the leaves. Not only was this creepy for the players (and therefore fun for the GM), but it got them involved. They wanted to know how it was done.
By hitting them with a spell of this nature, they were at a complete loss. They had begun to rely on a power that had been unleashed in the game. Instead of trusting to fortune tellers, they had to trust their own instincts. Of course, the enemies had fortune tellers, and by that time, the GM had learned several tricks on how to use them (from the players). Never hesitate to use a player’s ideas against them. At least make sure you use one group’s ideas against your next group.