The rules concerning the items are simple, but the way the items are created is not clear (i take my informations from the 20th anniversary edition)
The vampire can create a simple form (in the case i'm considering a wooden stake) without rolling and can spend 3 blood points to make it permanent.
My question is: where does the object appear? I guess they cannot summon an item from a hundred meters away, but should another vampire be close, say five meters, could the Tremere vampire summon a wooden stake in the other vampire's heart? Or inside his pocket to hide the fact that it's been summoned?
Given the circumstances it could be very tricky but powerful, though I would understand if it's considered too much.
I wonder if there's an "official" explanation in a rulebook somewhere or if it's only up to the storyteller.