It's a simple example of how I would implement a fireball. But the more I think about it, the more complicated it gets. What if a character didn't have complete immunity to fire as their defense? What if it was only 1/2 damage? Or -5 damage?
What if it wasn't damage at all, but an effect that was kicked off at the beginning of a specific phase? Or a temporary effect? Or something the character was carrying that was affected, not the character itself?
So many variables, so little time...
