Shadowcaster is okay? Awesome. I've been wanting to try one out for a long while...
I'm think along the lines of this:
Human Shadowcaster 6/Master of Shadow 3
He'd mainly focus on control/messing with opponents, and sometimes letting loose with a Reach Umbral Touch as a little ranged attack, that also happens to slow the opponent. And his big Shadow Elemental buddy could do hit-and-run stuff.
(I realize he's not so much a ranged blaster, but his Umbral Touch can be quite nasty and his area control mysteries can immobilize, weaken and otherwise hamper groups.)
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Easy-going and chatty, though generally he tries to draw attention away from himself. Somebody who likes to experiment, but also can have a mean streak and toy with enemies, if he thinks they're weak and simple. He would see treasure as a means to an end, not caring too much about it. Very dedicated and loyal, seeing it as his duty to fulfill his mission, or die trying.
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Background would be more in line with the first option. He would have been selected for his stealth and subtle magics.
I have a couple more questions concerning this, though...
1. Given the mystery advancement of Master of Shadow, would you be willing to say his Apprentice mysteries are now spell-like, or would that be considered a class feature of Shadowcaster?
2. Would the Favored Mystery feat grant an extra use of the mystery per day, as it does advance the way it is cast (and according to the text, that grants extra uses)?
(And would you be willing to take a look at some proposed patches by the class designer? They're here on EnWorld, right
here. If you say no, I don't mind.)
And if these questions are a bit too much, I can change my character around. Nothing's really set-in-stone as of this point.