Thunderstone

The caster charges a stone with energy and shoots it towards an enemy. Make a ranged spell attack against the target. On a hit, the target takes 6d6 Lightning damage. When the stone makes contact the resulting lightning causes 4d6 more thunder damage in a 15ft radius of the target. Targets in the radius must make a dex save to hopefully reduce the dmg by half

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the lightning damage increases by 1d6 for each slot level above 3rd.