This spell costs less to cast if it targets an attacking creature.
Target creature's owner puts it on their choice of the top or bottom of their library.
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Run Behind's first ability). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.
less to cast if it targets an attacking creature.