You conjure a blade of magical force in the air, which lashes out at your foes. Make a melee spell attack against a creature within range. On a hit, the target takes 1d10 force damage. The blade remains in existence for a short time; until the start of your next turn, you can make a single strike with your mystical blade as an opportunity attack.   You can make 1 additional attack on your turn at 5th level (2 attacks), at 11th level (3 attacks), and at 17th level (4 attacks).