well most blissey's would switch out once gengar comes in, but yes that set would of course own blissey... maybe not ohko so watch out for counterbliss
any decent phys attacker will take care of Blissey -_-
Cloyster is nice to use to possibly lure it out and explode as well... ice beam something until blissey comes in (if it does) then spikes just to be sure he doesn't switch to the oh so friendly dusclops, explode if it stays in
dugtrio spits in blissey's face btw
EDIT: also pokes with 404 HP can throw up the 101 subs and cause blissey some problems
EDIT: dugtrio spits in Blissey's face twice.. then blissey kisses the floor