From NexusClash Wiki
This skill grants the character immunity from the damage caused by the inherent nature of other planes of existence called Planar Damage. Certain planes will cause damage to a character just for being present there -- this skill negates that damage.
During Breath II it also negated Infusion Damage, the damage a character would take from passing through tiles infused by hostile factions. Infusion Damage was a product of Tlacolotl's influence on that Breath, and so has since been removed.