The spell created three whistling darts of magical energy that shot at targets of the caster's choice in a twisting motion. Unlike the darts created by magic missile, these did not automatically hit their targets and had to be properly aimed by the caster. However, if they did hit, they caused considerably more damage than the ordinary magic missile darts, with a chance of even greater damage on a particularly good hit.
The less stable magic of Jim's magic missile also presented a risk to the caster. There was a small chance that the spell caused the darts to explode in the caster's face, dealing a small amount of damage.