This is a tribute to both the Swamp Thing film and the 2nd Batman Unlimited title. It ended up working out as a double tribute because Swamp Thing looked pretty bad in his film while Batman was giving people the work in his. Swamp Thing is pretty tough since he works with the Green and has a good amount of super strength. Still, it won’t be enough against Batman and his many gadgets. Once Batman pops on his GL Power Ring then the match is really over. Batman wins.
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I think they have fought in the comics before and Swamp Thing won. You can’t get rid of him unless Batman is prepared to destroy all planet life on Earth.
That’s true, Swamp Thing won their encounter, but Batman did seem confident that he would win next time. If they were to fight with no prep time then I think Swamp Thing definitely wins, but with composite Batman gets access to many different abilities which would let him essentially destroy the Earth if he so desired