Death dive. When the wisp dashes any creature is within 5ft of them during the movement takes 6 (2d6) necrotic damage. 

Regeneration. The wisp regains 5 hit points at the start of its turn. If the wisp takes radiant damage, this trait doesn’t function at the start of the wisp's next turn. The wisp dies only if it starts its turn with 0 hit points and doesn’t regenerate.

Spawn wraith. When the wisp drops a creature to 0 hit points the creature dies and is rises as a wraith and keeps there initiative count they originally had but is loyal and would die for the wisp. 

Multi attack. The wisp makes two shadow bite attack. 

Shadow bite. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: 9 (1d10 + 4) [Necrotic damage] damage and the target also has disadvantage on constitution saves and strength saves until the end of there next turn.