Eldritch Invocation: Temporal Leech

When you hit a creature with an Eldritch Blast, you can sap its temporal essence. Once per turn, choose one beam to trigger this effect:
• If the beam hits, you or an ally within 30 ft. regain hit points equal to half the damage dealt (rounded down).
• Alternatively, force the creature to subtract a d4 from its next attack roll or saving throw.