In the audit menu of the arcade version, there is a useless row of text that says "ERMACS" (which stands for Error Macros) and is listed under "Reptile Battles." Because of this, players thought that Ermac was a hidden boss like Reptile. Ermac became a running joke for the developers, so much so that they even made him a real character for Ultimate Mortal Kombat 3, with his BIO saying he was hiding in the first Mortal Kombat.
Contributed by gamemaster1991