Phantasmal Force

This extremely flexible spell allows the magic user to craft a visual illusion of virtually anything that can fit within the spell’s area of effect. The spell creates no sound whatsoever. The caster must maintain his or her concentration upon the illusion, or it will evaporate, but while concentrating the caster is able to make the illusion move and respond to events.

The illusion is dispelled if it is struck with a blow, a falling person, etc. There is no saving throw against the illusion if the observer believes it, and the illusion can actually cause damage to such a deceived victim. A demon wielding a sword can attack and do damage, and the appearance of a pit full of spikes can be fatal even though it is not real. If the observer doubts the reality of the illusion, he or she will be permitted a saving throw to see the illusion for what it really is. If one observer disbelieves the illusion and this disbelief is communicated to others, the others will also gain a saving throw at a bonus of +4.

Note that the spell relies purely on a visual effect; it will have no effect upon a creature that does not see it. Furthermore, the lack of any audible component can make certain illusions completely non-credible. An explosion, for example, is not likely to be believed by anyone if it creates no sound. Various methods may be used by the GM to determine if an NPC or monster believes the effect of a phantasmal force, common sense being the first thing to consider. A player who takes care to craft a believable illusion should be rewarded for skilful use of the spell, not forced into a table of random results.