Mortal Kombat 11

Fatalities for Erron Black:
Even if the 2nd fatality is locked you can still use it

Melted (Mid) - Down, Down, Down, X

Death Trap (Mid) - Down, Forward, Down, Y

In this video guide I will show you how to perform two different fatalities with Erron Black. For the first 10 characters I just used the klassic towers to get the achievement progress for I Want It All. Make sure to put it on very easy to make things quicker. Also pick the shortest tower.
After getting your I Want It All achievement the method with be a lot faster. Once in the main menus press the start button to go into the options menu. Scroll down to change the rounds to win to one. Then back out, go into the fight menu, select local, make sure to press X to turn on the CPU, and then select your character. You only have the one health bar to deal with to get to the fatality.
Achievement progress also counts if AI do a fatality.

Melted (Mid) - Down, Down, Down, X
Death Trap (Mid) - Down, Forward, Down, Y

In the options (press Select) set number of rounds to 1 and when selecting opponent set AI difficulty to 'Very Easy' (can also use a second controller if available).

Hit the enemy until their health bar is drained at which point 'FINISH HIM' will appear on screen. Position your character in the appropriate spot and input the following commands:

Melted (Mid) - Down, Down, Down, X
Death Trap (Mid) - Down, Forward, Down, Y

Then when the points are tallied hit 'Retry' to restart and perform the second finishing move.