Witch Bolt

1st-Level Evocation
Casting Time: 1 action
Range: 30 feet
Components: VSM (a twig from a tree that has been struck by lightning)
Duration: (C) 1 minute

A beam of crackling, blue energy lances out toward a creature within range, forming a sustained arc of lightning between you and the target. Make a ranged spell attack against that creature. On a hit, the target takes 1d12 lightning damage, and at the start of each of your turns for the duration, you deal 1d12 lightning damage to the target automatically. The spell ends if the target is ever outside the spell's range or if it has total cover from you.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the initial damage increases by 1d12 for each slot level above 1st, and the damage on subsequent rounds increases by 1d12 for every two slot levels above 1st.

Source: PHB 289

Changelog

Altered upcasting to deal additional damage on the subsequent rounds for every 2 slot levels above 1st.
No longer requires an action to damage on subsequent turns.