In Mortal Kombat 11, you can punch someone in the back of the head so hard their brain ejects through their face. You can summon a magic wall of sand, stick someone into it, and then rip the entire front half of their body off with your bare hands. You can also, if you're playing as Jax in the game's Klassic Towers mode, watch a short character ending in which Jax goes back in time to prevent the Atlantic slave trade.
The ending is being called 'controversial,' though as far as I can tell, most people think it's pretty cool.
You can watch the scene above—it has nothing to do with MK11's campaign, and is more in line with the short scenes that cap off character "stories" in most fighting game arcade modes (like this classic from Mortal Kombat 4, where Jax throws Jarek off a cliff). All of MK11's endings consist of a few shots of static artwork and a short voiceover, as the characters decide how they'd use the power to manipulate time (the reward for defeating new villain Kronika).
Unlike a lot of simpler or more frivolous endings, Jax's tackles a heavy subject in its short running time and is unsurprisingly vague on the details. Here's pretty much all we get from his voiceover:
"I've been lucky. My family and I have lived the American dream. But most people who look like me haven't had that chance. I owe it to them to put things right. And I'm not waiting centuries for people to get woke when I've got the power to speed things up. I don't get it right the first time, or the second, or even the third. But eventually, I knock it out of the damn park. My family's back. The world's a better place for everyone. Turns out, you CAN have everything. Anyone who says you can't needs to dream bigger."
Through presumably many attempts to go back in time and kick off the exact right sequence of events, Jax eliminates slavery and lives happily ever after. It's vague and glosses over time travel paradoxes and so on and so forth, but this is also a game in which Johnny Cage rips someone in half and makes their bleeding torso talk like a puppet. Jax's ending may be more serious than most of them, but seems like a perfectly sensible move for someone with power over time.
Looking through forum discussions and Reddit threads, I've mostly seen praise for the ending's idea and the occasional complaint that it's a ridiculous thing to get upset about. Some coverage of the ending has highlighted the negative reactions, like "Some 'Mortal Kombat 11' Fans Are Calling Jax's Ending 'Racist,'" "Jax’s Ending in Mortal Kombat 11 Is Getting Some Disappointing Backlash," and "People Are Upset About Things That Don’t Actually Happen In Jax’s MK11 Ending."
But it's hard to pinpoint any real controversy over Jax's ending. Outside of some downvotes on Youtube, a few whiny comments here and there about politics in games, and negative user reviews on Metacritic mixed in with complaints about MK11's microtransactions and always-online features, the response has seemingly been, by and large: "Cool."
The "controversy" seems like mostly a case of manufactured outrage, as described by Youtuber Shaun in relation to Doom Eternal last year. Shaun breaks down how a few comments can be used to portray a larger trend that doesn't really exist, and how piles of Youtube accounts will use the same flimsy material to dream up a controversy that doesn't really exist.
Kind of like this.
The impetus for Jax's ending being widely discuss was, as best as I can tell, a joke from Twitter users BAKOON making fun of one of these stupid 'anti-SJW' videos. BAKOON has 64,000 Twitter followers. The Youtube video complaining about the ending comes from an account with a whopping 595 subscribers.
the black guy character in mortal kombat has an ending where he uses time travel to make it so the slave trade never happened, and the gamers are so angry. dont click this guys video, just laugh at him https://t.co/LgMF2m4smTApril 22, 2019
The point is, there's really nothing controversial about the idea in Jax's ending, because slavery is an indefensible practice, and only a few loud racists were ever actually mad about it. Far more people are critical of MK11's microtransactions and always-online requirement for some modes. There hasn't been much of a backlash about Jax's ending. It's not even the only Mortal Kombat 11 ending to reference slavery: Baraka's ending sees him freeing Tarkatans from slavery to conquer Edenia, Outworld, and Earthrealm.
If you want to see what the other characters in MK11 get up to in the Klassic mode, you can watch all of the endings back-to-back in the video below.