There is a Legacy version
here.
Siphon Life [two-actions] Feat 10Rare Aftermath Magical Void Source Dark Archives (Remastered) pg. 56Prerequisites You've been reduced to 0 Hit Points by an enemy with the
void trait.
Experiences with necromantic energy have left a permanent mark on you, casting you in a deathlike pallor, chilling your body temperature to be ice-cold, turning your very blood black, and giving you the power to rip out an enemy's life force. Strike with an unarmed attack. If you hit and the target is a living creature, it takes 4d6 additional void damage, depending on its Fortitude save. If the target takes any void damage, you gain an equal number of temporary Hit Points, which last for 1 minute.
Critical Success The target takes no additional void damage and becomes temporarily immune for 1 minute.
Success The target takes half the additional void damage.
Failure The target takes full additional void damage.
Critical Failure The target takes double the additional void damage.
Traits
Rare: This rarity indicates that a rules element is very difficult to find in the game world. A rare feat, spell, item or the like is available to players only if the GM decides to include it in the game, typically through discovery during play. Creatures with this trait are rare. They typically can't be summoned. The DC of Recall Knowledge checks related to these creatures is increased by 5.
Aftermath: This trait describes feats that represent special abilities gained after exposure to the weird and deadly.
Magical: Something with the magical trait is imbued with magical energies not tied to a specific tradition of magic. Some items or effects are closely tied to a particular tradition of magic. In these cases, the item has the arcane, divine, occult, or primal trait instead of the magical trait. Any of these traits indicate that the item is magical.
Void: Effects with this trait heal undead creatures with void energy, deal void damage to living creatures, or manipulate void energy.
Planes with this trait are vast, empty reaches that suck the life from the living. They tend to be lonely, haunted planes, drained of color and filled with winds carrying the moans of the dead At the end of each round, a living creature takes at least minor void environmental damage. In the strongest areas of a void plane, they could take moderate or even major void damage at the end of each round. This damage has the death trait, and if a living creature is reduced to 0 Hit Points by this void damage and killed, it crumbles into ash and can become a wraith (see Monster Core).