Energy Vulnerability

A weapon etched with this rune has a sheen of a color corresponding to the energy type chosen when the rune is created: green (acid), blue (cold), white (electricity), orange (fire), or yellow (sonic). When you critically hit a target with a weapon with this rune, the target gains weakness 5 to the chosen energy type until the end of your next turn. This weakness isn't cumulative with any weakness to that energy type the target already has and doesn't affect a creature with immunity or resistance to that energy type.