Who says ball of lightning isn't the best dragon ability?

[DGDobrev]

Peacefulness increases the HP of a troop. Since Ball of Lightning bases it's damage on the HP of the victim, you can imagine why - the max damage is 48% of the total troop health. With mark of blood it can kill 96% of the enemy troop max. I think I got close to that here - about 90% of it.

Here's how a simple stupid spell that barely someone uses may become a really powerful weapon against enormous stacks.