When using a Fatal Blow, it will have armor after the first 5 frames of start-up. Johnny Cage has the unique ability to cancel out of his Fatal Blow. This will allow Johnny Cage to gain armor while cancelling into an attack. For example, Johnny Cage can armor through the gap in Scorpion’s +, by using his Fatal Blow then cancelling out of it.
Note: As of January 21, 2020, Fatal Blows can no longer be used to interrupt 5 frame gaps. There must be at least an 8 frame gap in a string in order to use a Fatal Blow.
The reason why this can be useful is because Fatal Blows only have a one-time use per match. If you do not want to use up your Fatal Blow, you can cancel out of it and save it for the next round. Another great thing about this is that if the opponent blocks, then you will be able to pressure your opponent, whereas if you didn’t cancel the Fatal Blow then you would be punished. Essentially, cancelling out of Johnny Cage’s Fatal Blow will act as a parry that leaves you safe and counter any attack with the use of armor.
The only downside to this is that if the opponent has Defensive Meter then they can use a Breakaway to escape your combo, in which case it would be better to not cancel the Fatal Blow for unbreakable damage.
Johnny Cage’s Fatal Blow cancel is very situational, but can be rewarding when used correctly.