To unlock the Secret Endings in Killer Instinct on the Xbox One you have to beat Shadow Jago.
--How to fight Boss Shadow Jago--
First you need all 3 Endings of one character unlocked. (Check under Fight Archive = Cinematics) Then you must Beat Arcade mode on Medium Difficulty or higher using the character who's endings are unlocked. You must not loose any match, and you must perform an Ultra on Enemy #6 (Rival). If done successfully, You will skip fight 7 (Fulgore) and go to Secret Fight 8 Instead.
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