Eldritch Impalement

The user summons a wave of Eldritch magic, and teleports behind an enemy within sight at most 300ft away, the user can then make a melee attack with a weapon or a Eldritch knife that does 2d12 piercing damage, advantage or disadvantage is applied and the attack will instakill if the CR of the creature is less that the players level. If it does instakill, you can either stay in your location or teleport back to the spot you casted the spell from as a bonus action, if it doesn’t, the enemy must succeed a DC 18 wisdom saving throw or be surprised for 1 turn.