Suggested by Sonic Whispy Woods is a pretty powerful tree and I’m sure Swamp Thing would be proud to see such a powerful plant. Still, Swamp Thing is leader of the Green and is incredibly powerful. He has traded blows with powerful fighters like Superman and Wonder Woman in the past. I don’t really have any doubts that he would be able to overwhelm Whispy Woods with minimal effort. Whispy isn’t very mobile and lacks a lot of attack options. Swamp Thing would likely break him with a punch or two. Swamp Thing wins.