How to defeat Vittorio and his ballista?

Thanks, Flandre, I noticed that too)))))

Added after 23 hours 1 minute

You take Grol, develop his Deadly Cold (he starts with a developed Chaos skill), teach him Stone Skin or Ring - and Vitkina's ballista will be resting...

That sounds a bit doubtful. I still won't kill her in the first turn with this method, and as a result, my hero will spend his turns on her, while she and her hero will take me down. Honestly, this isn't a very good option. We're playing on "Former Friends".