The Sentry: hyped as to what he could do, but never really has actually done (eg, if the power of a million exploding suns had really happened in WWH, there'd have been no solar system left).
Dr. Manhattan: existed for a dozen issues in a story not crafted for power display. We get hints of what he can do, but again, nothing a handful of other characters couldn't also do.
Thinking inferentially, extrapolating beyond on-panel showings and statements, what would be a top feat for either character, something which really cements home the scope and depth of their power?
Who'd win in a fight?
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Shinier than a speeding bullet.
Nah.
He sees the past, the present and the future as if it were seconds.
But there are things that are meant to happen. Thus he did not bother stopping the events that unfolded in Watchmen series.
He didn't really give a damn about us petty humans anyways.
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"Farewell, Damos... Ash, Pikachu... And you. All of my beloved." -- Arceus
No, he's not. He says so himself in the interview, prior to being accused of being carcinogenic.
His view of the future was blocked by tachyons, he didn't know that certain friends/enemies had cancer, he was surprised by the result of Veidt's plan unfolding. All of these things imply lack of omniscience.
Sentry has held the power of a cosmic cube and brought a person back to life with a wave of his hand. Dr. M created a city out of nothing and stated that he might create his own species of life.
the good dr wins. cant hurt what you cant touch. between intangability and producing clones of him self, he will confuse the shit outta sentry. Physical abilities are not enough for the blue penis! Creating life is not a issues with DR M at least in the movie. He even claimed to go off to another galaxy to start to create life or at least that was a idea he had. HE can also increase his size and im talking about hieght not his dick.