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The way Dragon Ball power levels is allocated into "stats" is really fucking weird because characters can casually destroy planets and move faster than light in bursts, but they're very clearly susceptible to the elements, like how the Hyperbolic Time Chamber was hyped up by having extreme temperature shifts and characters from Monster Rabbit to Buu show that pretty much everyone in the setting is incredible weak to "magic"
So in pure theory Mewtwo COULD probably win with some elemental attack like that or some other non-standard fuckery but in practice it's going to Freeza, especially since Freeza is weirdly durable for DB standards