Ambush

Flash through the shadows and teleport to an open space behind any creature you can see within 30ft, striking them for 1d8 slashing damage. On a hit the target makes a CON saving throw or they are stunned until the start of your next turn. (You must be wielding a melee weapon to cast this spell)

Increase the damage by 1d8 at 5th (2d8), 11th (3d8) and 17th (4d8) levels.