Petrification can refer to the condition, or to the odd ability of certain Pretender God chassis to inflict it. A Petrified fellow is a statue; they are entirely helpless, but they also have a minimum of 20 Natural Protection, along with Pierce Resistance and Slash Resistance.

The Petrification trait is a defensive ability, like Curse Bestower or Sight Vengeance. The Gorgons (Immortal or otherwise) are the vanilla possessors of this trait; when a fellow attempts to attack them, they must look at them, witnessing their horrific visage. Instead of destroying their eyes (like one with Sight Vengeance would), this petrifies them, like in the myths of Medusa. Unlike in the myths, this effect can be resisted with a Magic Resistance roll; this is an Earth effect, and the base Penetration of this trait is 12.

Like in the myths, attacking a Petrifier from behind is safer than attacking them from the front or the side; there's only a 25% chance of being turned towards (in time) and seeing the petrifying face.

Does surviving the battle while Petrified mean you'll be okay? Maybe. When the spell ends via the end of battle, the Petrified fellow must succeed in a Magic Resistance roll against a Penetration roll with a base of 13, or else they'll be magically "instakilled" (as in, they'll remain a statue forever, unless they have Extra Lives or something). This is also an Earth effect.

The Penetration roll modifiers for Petrification are applied weirdly. According to Loggy, only the Penetrator's Earth skill applies upon the actual Petrification, while only the Magic Resistor's Earth skill applies upon breaking out of the magic.

Petrify is also a Level-6 Alteration for 5 mages, stopping a whole square of fellas. There is no roll for resisting the Petrification, but the roll for avoiding the "instakill" at the end of the battle still applies. The Priests of Earth Pretenders can also petrify with Word of Stone, but this one does have a roll for resisting.

Oh, and Cockatrices have Petrifying Breath! They're Cross Breeding results.