The two-and-a-half minute trailer appears to showcase just about everything Batman's greatest foe can do, from general dickery to a few fatalities, with his pixelated opponents sacrificing themselves so that you can see his full repertoire of moves.
One expects it won't be so easy in-game, but it looks cool in a string of clips:
Joker's character was first shown in 2019, the year MK11 was released, along with five other fighters, one of whom was the Terminator T-800. As GameSpot highlights, the Joker is now the second guest fighter from the current Kombat Pack. In addition to T-800, the other four characters will be Spawn and longtime MK staples Nightwolf, Sindel, and Shang Tsung. Note that those last three don't qualify as guests though.
Depending on how far back you go with Mortal Kombat (like, say, to 2008) it may not be a huge shock for you to see Joker cross over into the MK or NetherRealm universe. In fact, the iconic villain was in the Injustice games, which were also developed by that studio.
Though, made clear from the trailer above, he's not going to be censored by a Teen rating here.
In addition to now being able to play as the Joker (if you contributed to the necessary evil that is DLC...hey, developers gotta make a profit) you'll also have access to new costumes. After all, if you thought characters in the trailer looked a little different, you were not mistaken. Kitana has a costume inspired by Catwoman, Baraka can be seen as Killer Croc, and Noob Saibot makes a cameo as the Batman Who Laughs, among others.
As you can see from the embedded tweet the Joker will be available for Early Access customers by Jan. 28, and for everyone else by Feb. 4. After he joins the roster the only other character set for release is Spawn, who will get his day in March. That will wrap up the current slate of bonus fighters for the game, but it's been rumored that others could be added via a future fighter pack.