I stumbled upon a Nintendo Life review of Mortal Kombat for the Game Boy and the writer (Dave Frear) found little to enjoy in his critique:
Back, back, B. That’s the command that you need to enter to perform Scorpion’s spear move – but you have to do it slowly. Forget the quick tapping that you’d expect for a beat ‘em up, this is something with which you must take your time. It’s the same for all the special moves in the game, an irritant that’s just one of the many problems found in this Game Boy port of Mortal Kombat.
Switch your system on and the first thing that you see are some logos accompanied by silence. Enjoy the peace and quiet, because soon “Midway Presents” appears on screen and the horrific noise begins. A distorted combination of scratches, whines, beeps and ringing come together to create a truly awful audio experience. Some other Game Boy games may have music that’s beepy or a bit whiney, but it usually maintains a kind of charm. This, however, is just painful. There are a couple of tracks that play during the main game which are just as bad. Further scratches make up the sound effects, but the music tends to drown these out.
I actually thought the review was lighter in tone than the score suggested (spoiler alert: he gave it 1 star) but I take his points: Mortal Kombat was slow as hell and rendered the characters useless and samey. No need to tell me to avoid it, Dave—I already had for the past 29 years without realising.