When power word, kill is uttered, the character can either
target a single creature or let the spell affect a group.
If power word, kill is targeted at a single creature, that
creature dies if it has 100 or fewer hit points.
If power word, kill is cast as an area spell, it kills
creatures in a 15-foot-radius sphere. It kills only creatures who
have 20 or fewer hit points, and only up to a total of 200 hit
points of such creatures. The spell affects creatures with the
lowest hit point totals first until the next creature would put
the total over the limit of 200. (Creatures with negative hit
points count as having 0 hit points.)