“An immortal who has lived for centuries through the Lazarus Pit. He believes civilization must be reset for the planet to survive.”
Mystical waters that restore life from near-death or death itself — the source of his centuries-long immortality, at the cost of temporary madness.
Centuries of training under the world's greatest warriors. Generally rated at or above Batman's level in direct combat.
An elite global network of assassins. The organization that originally trained Batman — which is precisely what makes him dangerous.
Ra's al Ghul has watched civilizational patterns for centuries. The key is that he doesn't hate humanity — he pities it. The cold utilitarian calculus that billions must die to save the planet is what makes him the most dangerous villain in Batman's rogues gallery.