The Game Boy Color version of MK4 was developed by Digital Eclipse and was released by Midway. It is in 2D instead of the others' 3D. It features nine selectable characters: Raiden, Quan Chi, Fujin, Liu Kang, Sub-Zero, Reiko, Tanya, Scorpion, and the hidden character Reptile; Shinnok is still the final opponent. In addition, there are a few speech clips, and instead of using the in-game graphics for the Fatalities, the game uses short FMV clips. The Game Boy Color port's 2D engine reuses the game engine utilized in the Game Boy port of MK3, including the same character select screen, "Choose Your Destiny" screen, and how the characters move and interact. The background music was replaced with repetitive techno-ish songs with instrumentation befitting a Game Boy release, and the port does not contain any blood outside of the Fatality videos. The combo system and weapons were also removed. However, the graphics for the port were above average for a Game Boy fighting title, and it contains many of the arcade's backgrounds in vivid clarity.
Source: Wikipedia, "Mortal Kombat 4", available under the CC-BY-SA License.