Crystal's Arc Web

You imbue 2 creatures of your choice, within range, and who possess a rod of amber, crystal, or glass, with lightning energy. A bolt of lightning arcs in a straight line between those creatures as long as they are within 30 ft of one another.  Each arc is invisible until it deals damage and becomes invisible again after it deals damage.

When a creature crosses an arc for the first time on a turn that creature must make a Dexterity saving throw.  On a failed save it takes 1d8 lightning damage, or half as much on a success.

Once per turn, as a bonus action, you can cause a bolt to arc between each of the spell's targets.  Each creature in the line of the arc must make a Dexterity saving throw.  On a failed save, it takes 1d8 lightning damage, or half as much on a success.

At Higher Levels: When you cast this spell using a 3rd or 4th level spell slot, the damage increases to 2d8 lightning and the number of targets increase to 3.  When you cast it using a 5th or 6th level spell slot the damage increases to 3d8 lightning and the number of targets increases to 4.  When casting this spell with a 7th or 8th level spell slot the damage increases to 4d8 lightning and the number of targets increases to 5. When you cast this spell using a 9th level spell slot the damage increases to 5d8 lightning and the number of targets increases to 6.