Hiruzen was a master of over 1000 Genjutsu's, he Also has a 5 in Genjutsu
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He was known as "the professor" for Knowing and being able to use all known (Non Kg) Jutsu's in the leaf at one Point in time.
He has shown Fire and earth, I would say it's safe to assume he can also use Water, Possibly Wind aswell.
Also having a 5 in Ninjutsu
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Even in his old age he was said to be the strongest of the 5 current kages.
Kabuto has been a Spy from a Very young age, He has spied in every village since a child , and knows things others don't know.
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Hiruzen also has Mostly all 5's in his Databook Stats. Only lacking Speed/Strength/Stamina because of his Old age.
Proof os his Weakening in his old age. hiruzen was suprised how heavy Enma felt in his pole form
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Proof of his stamina weakening. One of the Anbu stats his chara has declined.
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Enma asked what was wrong with him and stated that he wasn't fighting like he normaly does.
Yet he was still able to hold his ground against two Kages.
Even in his old age, it was said he was Equal to Oro, when the manga had stated many times he is far weaker than his prime.
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Even Though Hiruzen was "Slacking" and Lacking his normal fighting prowess, He still was able to Compete with both Hashirama's and Tobirama's Taijutsu while planting Tags of them.
Even oro didn't notice.
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Enma has already Proved to be able to Counter Hashirama's wood style.
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He has already Countered bringer of darkness.
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Note: Look at the Page, and you see "Sniff", So hirzens sense of Smell must be quite good to be able to find Hashirama and Tobirama while he is blind.
Thats all i can be bothered to do at this point in timeU_U.
Also when Iruka said he is the strongest Hokage to the Academy students. Hiruzen replied with "Hey, Iruka!! Don't use past tense!!" Hiruzen IMPLIED he that he was the strongest in his prime. Plus Hiruzen was taught by both the 1st and 2nd. He'd probably know about their techniques and how to counter them. Heres when Sarutobi implied that before he was the strongest.
