Fireproof, like, really Immune to Fire Options

[Voran]

So critter power wise, 5th edition, Immunity to say, Fire comes at x2 Essence or presumably something like Force for spirits, and acts as a hardened defense. Tho apparently Spirits by default are not immune to their own element, so you can use a flamethrower vs a Fire Spirit just as well as if it were human.

Then you add Elemental Attack, which does x2 Magic with Magic rated Armor Piercing. So you also have situations where a Hellhound, immune to fire, can breathe on another Hellhound, also immune to fire, and reduce its Immunity to fire of 6, down to 1. (5 magic, 3 essence) And more often than not, do damage to the other hellhound with fire.

No idea what its going to look like for Dragons, tho base stuff give them potentially fire attacks of 20+ DV and 10 AP, and that's not even the 'legendaries'.

So if you were going to give immunity to fire, that was actually immunity to fire, what rating would it need to be? 30? 40? Elemental attack is a bit more potent in 5th, giving a bonus AP factor I didn't seem to see in the 4th, so roughly 50% stronger per given rating, assuming the target is armored.