I'll try and keep this short. Ask if you want an explanation on anything.

Plot: Mortal Kombat 12 takes place after the events of MK11. Liu Kang is now the keeper of time (the MK11 story ending), and is among the new Elder Gods consisting of Kitana, Bo Rai Cho, Kung Lao, and Raiden (his MK11 arcade ending). The rewriting of time has not gone unnoticed by the other Titans though, and Kronika's "sister" (the female Titan from Shang Tsung's MK11 ending) wants to destroy the new timeline in the name of revenge.

Main Roster:
Unnamed son of Liu Kang and Kitana
Unnamed daughter of Kotal and Jade
Scorpion
Sub-Zero
Cetrion
Shao Khan
Shang Tsung
Cyrax
Smoke
Sindel
Tanya
Erron Black
Kano
Cassie Cage
Jacqui Briggs
Takeda Takahashi
Nightwolf
Sheeva
Baraka
Ashrah
Sareena
Quan Chi
Sektor
D'vorah
Motaro
Reptile
Rain
Stryker
Kabal
Tremor
Skarlet
Nitara
Hotaru
Havik

Potential DLC Roster:
Blaze
Onaga
Meat
Chameleon
Pennywise
Brainiac

Possibly-unplayable boss: Unnamed female Titan (going by Shang Tsung's MK11 ending, she looked to have space powers, like the Pokemon Palkia)

Features:
- Multiple modes of play; Story, Arcade, Versus, Kombat Towers, etc.
- Krypt with the usual sort of unlockable content.
- Different uniforms unlocked through various means; these are merely cosmetic.
- Kreate-A-Fighter returning from MK:A, but now with far more extensive customization.