Warning: This article contains SPOILERS for Mortal Kombat 11's story.
The Mortal Kombat 11 ending is easily one of the most mind-blowing endings of any Mortal Kombat game so far. Not only that, but it's also an ending that will likely shake things up significantly in future Mortal Kombat installments while opening the series up to a world of endless possibility as far as what remains canon.
Mortal Kombat 11's story involves a new antagonist Kronika, who is the Keeper of Time, who seeks to restart the timeline and create something called the New Era. This new timeline would see Raiden erased and balance restored, which would mean endless war between the realms. The protagonists spend most of Mortal Kombat 11 trying to foil this plan, with younger versions of well known characters either teaming up with their older selves or fighting against them (depending on various circumstances) thanks to Kronika's manipulation of the timeline bringing the past and present characters together.
Near the end of Mortal Kombat 11's story, Raiden combines his soul with Liu Kang, essentially turning the latter into a god himself - he's called Fire God Liu Kang during this section of the game - in an attempt to defeat Kronika and stop her plan from taking shape. In spite of their best efforts, the duo fails and Kronika is able to restart the timeline. In spite of this, Kang and Kronika battle in an Earth before modern man in the time of dinosaurs (a T-Rex will attack at some point). This is where things get a little complicated. During the fight, there are technically three different endings a player can achieve.
For the best ending of Mortal Kombat 11, players will need to defeat Kronika in all rounds without losing once. In this ending, Kang will become a full on god while Raiden becomes mortal. Raiden then tasks Kang with being the one to influence the timeline and Kang will proceed to do so. He'll bring Kitana with him and the duo will essentially work together to ensure the best future possible, though Kitana warns that no matter what they do, evil will still pop up. The game then ends on a cliffhanger.
The middle ending, which requires players to only lose once against Kronika (which will see her teleport Kang even further back in time) and is nearly identical to the good ending. The only difference this time around is that instead of Kitana, Raiden himself vows to help Kang with the timeline, so long as his new-found mortality allows anyway. The bad ending sees Kang lose two times to Kronika, which will see a cutscene follow where the antagonist decapitates Kang. Luckily, players will get a retry option at this point, but it's still a neat little addition to Mortal Kombat 11's storyline.
It's unclear which ending will eventually be considered canon when an eventual Mortal Kombat 12 comes around, but most of the time in situations like this, the best possible ending will be bestowed that particular honor. Of course, that game is a long ways off, giving developer NetherRealm Studios plenty of time to decide how they want to tackle that particular wrinkle. Either way, giving Kang the ability to change time as he sees fit will allow the developers to have some fun with the next entry and play with the canon even more than they already have. Plus, Kang as a god will be an interesting twist (it's also a nice nod to the non-canonical ending of the 2011 Mortal Kombat game where Kang becomes a fire god). For this alone, Mortal Kombat 11's ending is a big cleaning of the slate moment for the franchise as a whole.