Only downside would be that it lasts only as long as you can concentrate. And one whack of a war hammer to see if it can be broken will allow a save, but hey, that's how the whole illusion school works :)
That seems a perfectly acceptable use of the silent image spell.
Note that the target would not be able to see outside (although I'm not sure how the lighting conditions inside the box would be affected), and those outside would not be able to see the target inside either without making an appropriate save.
I'm not sure that the wizards party members would automatically disbelieve either, though. Illusions are powerful because they can trick the senses, even with evidence that the illusion is not real; thats the reason for the saving throw, as those with greater willpower and wisdom are more readily able to disbelieve their senses. If I were the DM, and assuming the party members know that the spell cast was an illusion (and telling them out loud that it is might tip off the bad guys!), I'd give each of the party members an immediate disbelieve save with a +4. If this were a common tactic employed repeatedly, I'd eventually give the save immediately to the party members without having to be told that its an illusion. But I would never have the party members immediately disbelieve without making a save, as it is a direct trick of their senses, and such can be hard to overcome even with evidence to the contrary.
Also, I'm not sure how PF treats a disbelieved illusion. Can one who disbelieves the illusion see through it? Can the caster of the illusion?
In any event, it would be a useful tactic for taking a combatant out of combat for a round or so.
|
Unless the illusion creator specifically stated that the inside of the box was dark, as GM I would simply state that it appears illuminated from some unknown source.
And yes, unless the illusion creator described it as "opaque from the outside" then those outside would not see the "captured" target either. They would see the box until they interact with it etc.
In my campaigns in the past the illusion caster told me outside of encounters that he was going to spend time working with the other PC's helping them understand when he was casting an illusion. Sometimes this involved him using a special code-word, other times he would create an illusion he uses frequently that they would more likely be familiar with. In any event, I alway gave the illusionists party members a free save (no interaction required) with a +4 bonus due to his efforts to make them aware of it. Usually this helped one or more of them see through the illusion right away, some of the dumber PC's still failed regularly, which added a cool "limiting" factor to the spells utility level.
And it could be a useful tactic not just for a round or so but for however long the target fails to realize it is an illusion. If it were cast on particularly low-will targets they could be in there for quite some time.
