Mortal Kombat X released earlier this month to rave reviews, even though it's quite possibly the most violent, bloody iteration into the franchise yet. It seems that as time goes on we begin to become more accepting of the violence in video games, which may or may not be a bad thing. At any rate, Mortal Kombat has an exceedingly strong presence in the games industry. It's one of the older franchises, surviving the ebb and flow of time.
Most of the Mortal Kombat games have featured a secret battle that is only accessible after beating a certain enemy via "Flawless Victory." This is what you are presented with when you have defeated an enemy without losing any health. This can prove to be a huge challenge for some, which only serves to reinforce Mortal Kombat's status as one of the toughest fighters in gaming. Mastering its control scheme can take a huge amount of time and effort.
!Spoilers Below!
This secret boss battle can be accessed via the "Mortal Kombat 1 Living Tower." During the sixth battle, players will have to finish the fight with a flawless victory and kill their opponent using a Brutality or Fatality.
Youtuber JurrasicRabbit highlights the process here: