Fail Machamp if you're not OHKOing with Dynamic Punch. Actually, fail other player for leaving Blissey in to take a Machamp's Dynamic Punch. Also, Blissey gets Heal Bell, Aromatherapy, Softboiled, and even has Natural Cure, so status effects (especially Toxic) won't work.
Blisseys are able to take a critical Focus punch and Dynamic punch does much less damage, so either I've only fought hacked Blisseys or your Machamp is extra badass.
Use of natural cure and healing moves requires the other person to not be stupid like I said.....
Also never just toxic Blissey, do gay stuff like toxic, sleep, and snatch to shutdown any healing and maximize toxic's damage.