Hell of 1,000,000 Needles

The landscape fills with monumental filaments of metal. The needles lance into a cube 30 feet on a side within 500 feet. Each creature in the area takes 13d6 (17d6 at level 20) piercing damage, with a basic Reflex save against your class DC. Each creature that fails its save is impaled, becoming Immobilized until it Escapes (the DC is your class DC); a creature that critically failed is also off-guard as long as it's impaled. The hell remains until the end of your next turn, but you can Sustain it up to 1 minute. Using this impulse again ends any previous one. The first time you Sustain it each round, lightning crisscrosses the needles. Each creature in the area takes 3d12 electricity damage with a basic Reflex save against your class DC. Squares in the area are hazardous terrain. A creature takes 6 (7 at level 20) piercing damage for every square of the area it moves through.

Level (20th) The initial damage is 17d6, and the hazardous terrain damage is 7.