Blue's News notes that Mortal Kombat 40 is out now on Steam, and my how time flies: it feels like only yesterday that I was getting to grips with MK38. It's not Roman numerals, of course; it stands for Xtra Large, referencing the fact that this new version of Mortal Kombat X includes the game's two 'Kombat Packs', the latter of which hasn't appeared on PC before now.
Kombat Pack 2, as Joe noted back in August, includes the Xenomorph from Alien, Leatherface from The Texas Chainsaw Massacre, and two fighters I've never heard of: Triborg and Bo’Rai Cho. If you already own MKX, you can buy this new pack separately, or in a bundle that lumps both packs together. There are currently various discounts for XL-related stuff on Steam.
There's also a new patch to coincide with the XL bundle, which developer NetherRealm has detailed here.