Night Darts

On several occasions, I have been travelling with human wizard companions who find that some of their spells are rendered useless by the fact that darkness prevented them from targeting their victim. In light of that (Pardon the pun...) I have created a spell which allows you to cast a modified version of magic missile which does not depend on sight. Instead, it seeks heat forms. Unfortunately, this spell does have a couple of hang-ups, but I will go into more detail about that later.

When cast, a small, glowing, red dart appears before the caster. This dart immediately shoots out into the darkness, seeking the closest heat form to the caster. When it hits, it sears into the target's flesh, doing 1D4+1 points of damage. Like magic missile, these beauties always hit their target. There is no dodging of the darts, no hiding behind walls. They seek with uncanny accuracy. The caster starts with the ability to call one dart into existance and gains an extra dart for every two levels he gains.