This is my first piece suggestion, value may need to be changed to be really balanced. One of its sinergies would be wrath in my opinion because if enemy doesnt capture back the petryfied piece one of yours will get +5 morale. Lich would also benefit from this piece because of the extra morale.
I think other stunners (Hydromancer, Medusa, ...) still seem better, because thay can also kill, and this at +++ for 14 seems a bit much. The added value to enemy seems like I don't want to do it without making sure I kill it, so kind of losing the time-buying aspect of petrify. I do like the theme of value increasing, but this / current suggestion doesn't too appealing, maybe try some other twist with it.
As side note, it would be helpfull to add the description as text, images gets shrinked too much, need to save it to read.