Psionic Vampire (5e Feat)
From D&D Wiki
Prerequisites: Psionic abilities
You prey on the unaware, siphoning small amounts of energy from them.
You score a critical hit on a roll of 19 or 20. Once on each of your turns you may siphon energy from a hostile creature's misfortune to regain Psi points equal to your proficiency bonus. This may activate when you score a critical hit on a hostile creature or a hostile creature rolls a 1 on a saving throw vs your talent or disipline.
You may pool this energy and gain a use of a talent or disipline. When you have accumulated the desired amount of energy you may use a talent or disipline as a bonus action on your turn. When you finish a long rest, any energy in this pool is lost.