I know Santa Claus isn't real, but if someone asked me how to falsify the theory that he DOES exist, I'd be stumped.
"Falsification" came as a replacement for the earlier criterion of "verification". Exhibiting an item "verifies" that it exists. A problem is apparent with general/universal statements such as "all electrons are identical". No reasonable way is seen except to shift the burden of proof: a unique different electron would falsify the claim, but its discovery is left to the opponents. Thus falsification is for theories which make sweeping statements. Existential claims are to be accepted only when their object is exhibited. It is the people claiming that X (Santa, the multiverse, etc) exists who bear the burden of proof.