There is a Legacy version here.


Source Player Core pg. 463
Effects with this trait heal living creatures with energy from the Forge of Creation, deal vitality energy damage to undead, or manipulate vitality energy.

These planes are awash with life energy. Colors are brighter, fires are hotter, noises are louder, and sensations are more intense. At the end of each round, an undead creature takes at least minor vitality environmental damage. In the strongest areas of a vitality plane, they could take moderate or even major vitality damage instead. While this might seem safe for living creatures, vitality planes present a different danger. Living creatures regain an amount of HP each round equal to the environmental damage undead take in the same area. If this would bring the living creature above their maximum HP, any excess becomes temporary HP. Unlike normal, these temporary HP combine with each other, and they last until the creature leaves the plane. If a creature’s temporary HP from a vitality plane ever exceeds its maximum HP, it explodes in a burst of overloaded vitality energy, spreading across the area to birth new souls.