Heliana's Guide to Monster Hunting, pg. 498
7th ring Arcane, Evocation
A storm made of crackling lightning and arcanomagnetic winds appears in a location you choose within range. The area of the storm consists of up to ten 10- foot cubes, which you can arrange as you wish and last until the spell ends. Each cube must have at least one face adjacent to the face of another cube. As a bonus action at the start of each of your turns, you can remove one 10-foot cube, and place another 10-footcube adjacent to the face of another cube.
Each creature that starts its turn in the area or enters the area for the first time on its turn must make a Dexterity saving throw, taking 4d8 lightning damage on a failure, or half as much damage on a success. Each creature that ends its turn in the area must make a Strength saving throw, taking 4d8 force damage and being knocked prone on a failure, or taking half as much damage and not being knocked prone on a success. A creature made of ferrous metal or wearing ferrous armour has disadvantage on this Strength saving throw.
The area is difficult terrain for any creatures made of ferrous metal or wearing ferrous armour.
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