Seal Soul (3.5e Feat)
From D&D Wiki
 Seal Soul [Epic, Dark]
Your seal fate class feature has become so strong that you can absorb even the soul of the creature.
Prerequisite: Darkness Class Feature, Seal Fate Class Feature, Seal Life feat
Benefit: If a creature dies when this ability is used, then the dark knight can choose to restore his hit points to his the maximum hp.
Normal: When the dark knight scores a critical he/she can only choose to gain an amount of hit points equal to ½ the damage dealt.