Mortal Kombat 1

At the moment for this season that ends in 46 days as of today when ypu get to the final boss fight sub zero you can get a secret fight against him by being Milenna so this guide will only be temporary until the season ends so got to be quick enough while using milenna you have to flip stance 15 tines during this boss fight i done a few more to be on the safe side and also i highly recommend using the talisman Frostfart its a complete game changer for his final phrase which he can insta kill you with that one charged up move so once the 3rd phrase starts save all your frostfart points and spam him at the start of the 3rd phase and dont forget at the very end to kick the bucket of water at him at the very end once he goes to the other side of the screen or you will get killed once youve won you should get the secret fight against milenna i dont know if you have to win for it to unlock but i won it anyway my achivement didnt pop after this fight so i had to restart the game and it popped once i done another normal invasion fight so this guide will become useless after the 45 days is up this might need to keep being updated these new guides

Season 4:

MESA > Tarkatan Colony

"Chess Club" Endurance fight

Finish it with Brutality, so the final hit must be an uppercut (DOWN + Y).

Other option: Shop on the Gateway MESA". Sometimes there is a "Silver Mortal Kombat Dragon coin" item for 6.500 coins, which activate the Secret Fight after your next fight.

Expired >>>

Just in SEASON 3, so only 10 days remaining for it (until 28. February).

Main Menu > Kampaign > Invasions > Living Forest

Almost the end of the Living Forest Mesa, at the bridge there is a fight called "Final Surprise / Second Constable", it's level 20. Do this fight, finish with Brutality (the last hit must be an uppercut -> down + Y).
I tried 3 times and every time got the Secret Fight. Achievement popped.

I used Baraka lvl 30 with FrostFart talisman and Invincible Relic, but I think it must work with any character or setup. Good Luck!

Expired.

Season 4:

MESA > Tarkatan Colony

"Chess Club" Endurance fight

Finish it with Brutality, so the final hit must be an uppercut (DOWN + Y).

Other option: Shop on the Gateway MESA". Sometimes there is a "Silver Mortal Kombat Dragon coin" item for 6.500 coins, which activate the Secret Fight after your next fight.

Expired >>>

Just in SEASON 3, so only 10 days remaining for it (until 28. February).

Main Menu > Kampaign > Invasions > Living Forest

Almost the end of the Living Forest Mesa, at the bridge there is a fight called "Final Surprise / Second Constable", it's level 20. Do this fight, finish with Brutality (the last hit must be an uppercut -> down + Y).
I tried 3 times and every time got the Secret Fight. Achievement popped.

I used Baraka lvl 30 with FrostFart talisman and Invincible Relic, but I think it must work with any character or setup. Good Luck!

For this season (Soul Eater), you’ll have to get to Sun Do Festival (second to last mesa). Find the Trick or Treat tower (4 floors) and complete the first floor by uppercutting. Secret fight will trigger and you will fight Firefly. Beat her and the rest of the tower and the achievement will pop.