The question is similar to this one but the song I'm looking for is different. I'm looking for the song that started approximately at 12:28 in episode 722. It begins when Doflamingo begins speaking. The voices cover some parts, but I like the song a lot.
The OST you're looking for hasn't been released as of yet.
As of now, it's named "Doflamingo's Theme" and you can listen to it here.
I'll update this answer once the OST has been officially released.
here it is guys, i found it finally