Lightning is one of the nature transformations that allow the user to generate electricity from their body or create it. Lightning, is of the elements that not only causes damage, but should it strike your target it should also shock them, leaving your opponent vulnerable. You can also channel lightning into weapons, making them more deadly. Lightning comes with a lot of uses, there's streams, beams, armor etc.
Lightning is strong against elements like earth and wood, because the electricity travels through those and break them. I dont think lightning has a weakness. Water might be one, but the combinations that you can use with those two elements is great. Water can be used to increase the electricity's damage. If you use a lightning technique in combination with a fire technique, the electricity should be hidden in the fire, surprising your target. A kkg I know of is storm release, not sure if there;s more.