How to being Petrified?

For Encounters II Challenge.
Sulfur Vents, The Gorgon boss.
It won't Petrify me.

I'm just standing still in front of it, it performs melee attacks, fire breath and shooting. But don't want to cast petrify whatever I do (standing still close, at middle distance, running around, whatever).

I even thought it's freeze effect, so I removed Hrimnor's Resolve from head - same shit.

From Pantheon I have Lunaris + Gruthkul, seems they can't prevent petrify as well.


OK, question closed. Stupid Gorgon don't cast Petrify on full health, and I was too cautious with it and afraid to kill it too quickly :-)