The song played in the post credits scene is "Who Wants To Live Forever" by Queen, which originally appeared on the Highlander (1986) soundtrack. Rick specifically named this film earlier in the episode when he said that the decoy families annihilate each other following "Highlander rules", because "there can be only one" (Highlander's tagline).
During the post credit scene Wooden Jerry encounters two wanderers. One is a woodpecker while the other one seems to be a humanoid dolphin. This is a reference to the post credit scene of A Rickle in Time (2015). At the end of that episode, the time cop tells his colleague: "When you get to the dolphin people, you've gone too far."
One of the passwords Rick uses to shut down a decoy family is "8==D" Another is "80085"
The title is a play on Multiplicity (1996). Rick's line "Ever make a copy of a copy?" even comes from the film of the same name with Michael Keaton.
The alien spaceships are based on the squiddies in the Matrix movies.