Unlocks all characters, including DLC fighters like Joker, Spawn, and Terminator, as well as story-locked characters like Frost.
For skins and costumes:
NetherRealm has reduced the grind significantly since launch: mortal kombat 11 unlocker
The risk of a permanent online ban outweighs any time saved. While the grind in MK11 is real, using an unlocker violates the EULA and can lead to losing access to the entire game's online features. If you are on PC, consider using mods that only change local textures (safe for single-player) but avoid any tool that claims to "unlock all" server-side content. Unlocks all characters, including DLC fighters like Joker,