Once regarded an improbable oddity; the fighting game guest character has become an industry standard. The invasion of outside forces remains a controversial topic for hardcore fans of any series: Mortal Kombat has become a seasoned veteran of the crossover concept, accepting fights at home and abroad.

Kombatants were first establishing their crossover credentials as far back as the nineties. Characters like Sub-Zero and Raiden have lodged appearances in various series, including: NBA Jam, Unreal Tournament and The Grid. Scorpion made the latest Kombat crossover earlier this year, appearing as a Jim Lee designed downloadable guest in NetherRealm Studios' superhero fighter: Injustice: Gods Among Us. The ninja from Hell is expected to be among the pack-in content in November's Ultimate Edition.

In 2011, Mortal Kombat took a turn playing host to two well known guest fighters: Freddy Krueger (DLC) and Kratos (PS3 exclusive).