Despite being severely underrated (and died early), I consider Haku to be one of the most powerful villains in the narutoverse. He was a natural shinobi and I'm sure that if he didn't die so early into the franchise, much more of his potential power as a villain could have been explored. Admittedly though, he's not the strongest among others, but powerful enough to hurt more than a few ninjas at the same time.
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