Electric Spark is a Spell added by Roots. It is created with the base ingredient, a Poisonous Potato, Glass, Glowstone and Sugar Canes. When cast, it will create a Vanilla lightning bolt.
— Runic Tablet
The innate charge of a potato combined with the harmfulness of its poison create a highly destructive spell. Using the above recipe, you can create a spell that will simply strike lightning on a nearby block you look at.