Ulnae's Lightning Whip

You create a whip of lightning. Proficiency with a whip allows you to add your proficiency bonus to the attack roll for any attack you make with it. On a hit, the target takes 1d10 lightning damage. Hit or miss, the lightning cracks and then a thunderous boom appears. The target and each creature within 5 feet of it must succeed on a Constitution saving throw or take 3d6 thunder damage.

At Higher Levels. When you cast this spell using a spell slot of 3nd level or higher, the thunder damage increases by 1d6 for each slot level above 1st.