The original arcade Mortal Kombat (and MK2, MK3 and UMK3) were all written in assembly for the TMS34010 processor. No doubt ports of it to the Sega Genesis did use 68K assembler.

The TMS34010 was something like a CPU and 2D graphics processor combined. It has the ability to change its word size from anywhere between 1 and 32 bits with data addressable on bit boundaries. It's wild.

https://en.wikipedia.org/wiki/TMS34010

The arcade version of Mortal Kombat used the TMS34010.

The Genesis port ran on a 68k of course.