振りをする： to pretend (that you're rich, that you don't know who ate the fucking last piece of pie, that you're a real hard-core gangsta, etc.)
よそお＊う: to pose (as a teenager online) , to masquerade (as a human even though you are a vampire). But also includes FURI's meaning of to pretend (to be happy or whatever)
Basically, 装う means you're trying to dupe other people intentionally, but 振りをする means you're fooling your own self.
振るう： literally, to brandish or wave about something. Figuratively, to be violent (although you don't say 'mommy help, he 振るed me!' you have to say (violent noun) PLUSを振るう））, or to use your power in a aggressive way. (i.e. the English phrase 'saber-rattling.')