How to defeat Vittorio and his ballista?

Ugh, I'm so bad:D. What kind of a "stone" on a ballista?! You can't affect it with non-area spells:D. But you can kill the ballista with a ring if you have the "Deadly Chill" skill.

Guys, what are you smoking during breaks between games?:eek:
You can cast spells, including non-area spells (and not just "Stone," but also "Swarm of Wasps," for example, cast by a Warlock), on any unit.