Sworn enemy.

So, it works like a hero's turn, and the hero himself is pushed back on the scale, but does it hinder? Because we first cast our own spells (charge arrows, launch them, and then our ballista will start working, while the hero stands aside, wasting mana).
This is great – first, we cast 3-4 spells on cursed enemies, slowing them down with cold or meteorites, and then the ballista fires!