Lifesurge

This special ability can only be placed on melee weapons. A lifesurge weapon boosts and sustains the wielder's life energy while he is in the throes of combat. The wielder gains a bonus on saving throws against necromantic effects—including the ability damage, ability drain, and energy drain powers of the undead—equal to the weapon's enhancement bonus. In addition, whenever the wielder receives temporary hit points from any source, he adds the weapon's enhancement bonus to these temporary hit points; this does not stack for temporary hit points from multiple sources, and these points are lost if the lifesurge weapon is not being wielded.

In combat, the weapon's critical threat range is doubled against undead; this does not stack with the keen special ability or Improved Critical. Whenever a lifesurge weapon confirms a critical hit against an undead creature, it erupts with 1d8 points of positive energy (2d8 for weapons with a critical multiplier of ×3, 3d8 if it is ×4); the wielder may choose to deal this as damage to an undead target or to absorb half this amount as healing, with the remaining positive energy dissipating.