I would say Mewtwo would have a nice shot at winning, as Psystrike is a 2HKO on Blissey and Fire Blast is an OHKO on Skarmory, and Blissey won't get a Softboiled in as long as Mewtwo is staring her down. And even if Blissey lands a Toxic, she will be at too low health to be able to Softboiled...