Blissey can use Final Gambit normally. You just need to KO something with Accelgor's Final Gambit, give Blissey a Scarf and Copycat.We just gave Blissey Final gambit guys. That will probably need to be dealt with
On a more serious note, Final Gambit will let Blissey check all the powerful Special sweepers in the metagame. Snorlax also gets it.