Arc Cage

The sky cries out as lightning cascades downward, forming a cage covering a 20-foot radius at a point within range that you can see. Creatures entering or within the cage make a Dexterity saving throw with the DC equal to your spell modifier. On a fail they take 9d6 lightning damage and are paralyzed until the next round. 

If they succeed, damage is halved and they resist the paralysis. Creatures that are paralyzed can make a Constitution check against your spell modifier at the start of their turn to shrug off the effect.

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