Cast Croaking Counterpart by paying ({1} magic symbol) ({G} magic symbol) ({U} magic symbol) , creating a token copy of Mirror-Mad Phantasm that is a 1/1 Frog.
Activate the Mirror-Mad Phantasm token by paying ({1} magic symbol) ({U} magic symbol) , shuffling the token into your library and milling your entire library due to it not having a card named Mirror-Mad Phantasm in it.