Nail said:
The problem I see with this is by-passing the Will save/"must interact" mechanic. I'm not comfortable with that, as it needlessly neuters an already weak magic school. That's no fun. :\
I don't think it "needlessly neuters" Minor Image at all. It's 2nd level for crying out loud. That puts the Spellcraft DC at 22 if you're just seeing the effects; that's not easily overcome!
First, Spellcraft is Trained Only, so most PCs aren't even going to get the chance to figure it out before they interact with it and get the Will save they're entitled to for doing so.
Second, as a 2nd level spell you could cast it as early as 3rd character level, and a 3rd level typical opposed caster will have usually no better than a +3 IntMod, 6 ranks, and a +2 synergy for 5 ranks of Knowledge (Arcana) for a total of +11 (and only then if maxed, which implies that this caster isn't easily fooled by such illusion magic and knows what to look for in such cases; Reward the Player for his chosen abilities!
).That's pretty close to a 50/50 chance which I don't consider easily overcome.
Now, if you want to convince such a caster that you
really have cast a new spell then you need to use a much better illusion spell, one of higher level. When you do that the Spellcraft DC goes up accordingly making it that much tougher for novice spellcasters (or those with only a few ranks in Spellcraft if non-casters) to figure out that it's an illusion spell. However, a caster of similar ability is more familiar with magic in general and therefore still has a much better chance of recognizing it for what it is, even without interacting with it: an illusion.
If you run into an illusion specialist, they're going to likely going to be have Spell Focus (and GSF if you actually use that!
) making it that much tougher to make the Will save, but IMG I'd also apply that to the Spellcraft DC since I think that makes sense.
Just my 2 cents, of course; YMMV.
Thanks.
DrSpunj