Several champions' endings have them overcoming their problems and learning to be the best they can be. Of special note is Sabrewulf realizing that their will never be a cure for his Lycanthropy. Rather than giving up hope of ever leading a better life, he makes peace with his beastly side and embraces the fact that as a werewolf, he's free from all restraints he previously had.
Shadow Jago's got MANY reasons to be an Awesome Moment in and of himself:
First of all, while it wasn't a secret for long, lots of streamers were scrambling to find Shadow Jago's secret boss. As it turns out, you must get all three endings for the character of your choice and play that character again in Arcade Mode on Medium difficulty without losing a single match (not a round, just for clarification) just to REACH him. Once you sucessfully complete all those conditions, you skip right over Fulgore (maybe Shadow Jago destroyed him already?) and enter an 8th fight as a shadowy silhouette of Jago appears as your opponent with the name of "???".
Once you finally get to him, his intro already blows your mind. He ascends out of this weird shadowy void, before gently levitating back down. He snaps some shadow energy into his hands and shoots his opponent a dirty look.
And then you start fighting him, and then you realize you're gonna have a bad time. He's no mere reskin of Jago with hard AI: he's got the hard AI, but with completely new moves, including a divekick, a Sub-Zero like slide, and double fireballs. He will whoop your ass the first time you fight him.
Assuming you're not unlucky enough to get hit with an ultra or a normal move, Shadow Jago will put you out of your misery with a very, VERY unique animation called a "No Mercy". That's right, Killer Instinct's bringing back finishing moves, and what better place to start than with a Badass difficult boss? Shadow Jago dashes back and forth around his opponent, slicing them with his sword, before uppercutting them up in the air and pursuing them for one last slice before landing gently, as opposed to his opponent who just SMACKS onto the ground.
Shadow Jago's victory pose begins with a scary zoom-in of his disgusted eyes, as parts of the Shadow Tiger's Lair collapse around him. He throws a Shadow Endouken towards his defeated opponent (in first-person). Assuming you were finished with the No Mercy above, you get a bone-chillingly simplistic noise, as a blood-stained and metalic "ULTIMATE" appear on screen.
And once you eventually beat Shadow Jago, you are awarded a secret ending revealing the Big Bad of Season 2 and access to the Shadow Tiger's Lair in all modes.