You could always go with the Counter set... basically the same as the standard Blissey, but with Counter.
- Counter
- Aromatherapy/Heal Bell
- Softboiled
- Thunder Wave/Ice Beam
I think Counter Blissey is scarier than regular Blissey, since it completely pwned me once. Since virtually no attack besides a super effective STAB physical Fighting move can OHKO this beast, and because of her monstrous HP, Counter is a guaranteed OHKO on any physical sweeper (or even Wall with a strong STAB attack) that can't take Blissey down in a single hit.
Of course, it's more difficult to play, because you could die in the next turn if something fast comes out to finish you off (why Thunder Wave comes in handy; may give you the chance to Softboil in the next turn), but if played well she can massacre any physical sweeper. I mean, I've seen Blissey survive a Cross Chop from Electivire. And that's why I stress the attack has to be STABed and strong as hell to beat Counter Blissey.