There is also Scaly hide too which can be found in arkam and the rouge on the docks. They have negative effects like low low level blindness. It works for gates. so armor, Scaly hide, Iron skin, and stone skin goes to about -100 to -120 AC. This plus your armor would/should max it out. Used it on my Svirf Cinalas.

So -20 or -40 for iron skin. -20 for scaly hide. -40 for stone skin and -20 for armor. Yes, Yes, and yes.

It works really well against fighters and paladins. Almost useless against smart mages and shamans.

I will surpass God.