Glad I don't have a participant in this fight, so I can weigh in. This would be a long fight, as I think they're pretty evenly matched. Mardax's energy seems to have a heat based component, which is obviously bad news for plants. However, I think Wild Daisy would be able to last longer. I see her sending an army of plants to attack Mardax, and if he did manage to get some contact with her, she would just use her morphic body to change/adapt in the moment, and just keep coming. Eventually, I think Mardax's energy would run low, leaving him vulnerable.

Winner: Wild Daisy