Empty Body (Su)
Source: Pathfinder Unchained, p. 16
A monk with this ki power gains the ability to assume an ethereal state for 1 minute as though using the spell etherealness, using his monk level as his caster Classes 1 level. Using this ability is a move action that consumes 3 points from the monk’s ki pool. This ability affects only the monk and cannot be used to make other creatures ethereal.