See, I don't like the static DC since it makes it too easy for enemies to believe as well. I think one of the main points is for allies to be able to join in as much as possible, while big brutish monsters can't. Of course, the party fighter is left out, but anyway...
There would be very few occasions when that would benefit the enemy. Believing in solipsistic creatures means the enemy can attack the creatures, but it also means the creatures can attack back. The caster of solipsism will be in control of the creatures as if they're summoned monsters, so they'd have to use
charm monster spells or the like to take control of them. Even if they do manage to take control, the wizard can just stop concentrating on the
solipsism. The wizard can do the same for solipsistic objects, which would prove inconvenient if the enemies were chasing the party over a solipsistic bridge or the like.
Hmm, should we allow the wizard to stop concentrating on one element of a solipsism (e.g. a single creature) while continuing to concentrate on the rest?
My point about Concentration is that I don't think additional believers should have to Concentrate to keep on believin'. Once they make their save, that should be until the spell ends.
That would match the original spell description, so I don't mind changing it.
Revising...
Solipsism
Illusion (Shadow)
Level: Sor/Wiz 6
Components: V, S
Casting Time: 1 standard action
Range: See text
Effect: See text
Duration: Concentration
Saving Throw: Will disbelief (Special, see text)
Spell Resistance: Yes; see text
You use material from the Plane of Shadow to shape quasi-real illusions of one or more creatures, objects, or forces. Solipsism can mimic any sorcerer or wizard conjuration (summoning) or conjuration (creation) spell of 6th level or lower, except its duration is as long as the caster concentrates. The illusory objects, forces, or creatures created by
solipsism appear to be transparent images superimposed on vague, shadowy forms.
Solipsism is the opposite of normal illusions in that creatures must make an active effort to believe (rather than disbelieve) in the illusion to be affected by it. The spell has no effect on those who do not believe. The objects and creatures "conjured" by solipsism become real to those who believe in them, with all the normal properties their form and function allow. Thus, a solipsistic
wall of stone bridging a chasm could be crossed by the caster and those who believed. All others would see the caster apparently walking out onto nothingness. Likewise, a solipsistic
summon monster spell can create a creature that can carry believers on its back, or attack believers to cause real damage.
The caster of
solipsism automatically believes in the reality of their solipsistic illusions. Other characters must deliberately try to believe in the illusion and succeed at a DC
16 Will save to be affected by this spell. A failed save means the character cannot convince themselves of the illusion's reality and the
solipsism has no effect on them. A character can make a single attempt to believe each round.
Once they successfully believe in the
solipsism, believers will continue to be affected by its "conjurations" for the duration of the spell. Believers can automatically stop believing in the
solipsism as a free action, but if they do so and decide to "re-believe" they need to succeed at the Will save again. The effects of solipsism continue for as long as the spell's caster maintains concentration. The caster can dissolve discrete elements of the illusion (e.g. a single creature out of a group, or one arrow in a quiver, but not part of a single object or creature) while continuing to concentrate on the rest of the solipsism, but such dissolved elements can not be re-believed into pseudo-existence except by casting the spell again.
Objects automatically fail their Will saves against this spell.
