Arc Lightning

You connect your hand and a target with a bolt of lightning. Make a ranged spell attack. On a hit, the target takes 1d10 lightning damage. On a critical hit, the bolt arcs to another target, causing it to take half of the original damage of the bolt. 

This spell's damage increases by 1d10 when you reach 5th level (2d10), 11th level (3d10), and 17th level (4d10).