Chromatic blade

You conjure a shift mass of energy to cut a target creature. 

When you cast the spell, and as part of each of your turns thereafter while the spell lasts, you can make a number of melee spell attacks with the blade (see the table below). Each attack has a reach of 5 feet. On a hit, the target takes 3d8 damage of the chosen type. The blade counts as a magical weapon for the purpose of overcoming resistance and immunity to nonmagical attacks and damage. The weapon vanishes if concentration is lost.