Mercer frustrates me, while I never liked his character, I was a fan of his powers, to the degree where I think he could be a pretty solid match for Dante, some of his abilities are really quite impressive.
Mostly though, I think it's his Shield ability that would give him a fighting chance, considering he's able to shapeshift his body into such a state that can actually negate all damage from anything that anyone throws at him.
That, and taking his devestator abilities into account, like his Tendril Barrage and Graveyard Spikes, he'd be able to do a significant amount of damage to Dante.
That being said, Alex Mercer is also stated to be the single most powerful character out of any comic book and videogame, so...I'm siding with Mr. Mercer this round.
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