Invulnerability is a somewhat-rare trait that makes bare skin tougher to penetrate by mundane means. If a fellow's Invulnerability score is higher than their Natural Protection and they are hit by nonmagical damage, their Invulnerability is used instead of their Natural Protection.

Individual application of Invulnerability is an Alteration effect, changing the nature of the skin. 11 mages can cast Stygian Skin to Achilles themselves for 15 points, while 3 mages can cast Invulnerability to give themselves a Demilich's 25 points. Alternatively, Evocation allows 32 mages to cast Stygian Rains with 2; this gives everyone in the battle 15 points, on top of making it Rain.

Two nations, Sauromatia and Marverni, have units with dormant Invulnerability from Magic Tattoos. A 11 mage with Enchantment knowledge can cast Awaken Tattoos, providing them 10 points and some other effects.

Multiple sources of Invulnerability do not stack.