Sasori wins low difficulty. If any buffoon surmises the thought of Byakugou mitigating the poison, then I will virtually beat you with my fists. Byakugou multiplies pre-existing cells in an attempt to heal wounds; cue when Madara stabbed Tsunade but she regenerated. Poison is internal, and reproducing your cells would be counter-productive as you would be reproducing the cells that already have poison that is surfaced... further hastening the poisonous effect. Beyond that, even if for some apparent reason, someone decides to give Tsunade an antidote, she has nothing to deal with Satetsu magnetizing her on imminent contact and making her a sitting duck for demolition at the hands of any of Sasori's attacks within his wide and vast hidden arsenal.