Boon noted that if a character is discovered to be too powerful, or if an inventive player discovers an infinite combo, developer NetherRealm is able to "make adjustments and address those things immediately." Precise details on how this works were not revealed, with Boon stating only that the dynamic updates are "built into the system" and don't require a patch.
Mortal Kombat isn't the first game to utilize dynamic updates. Certain Xbox Live Arcade games have managed similar on-the-fly updates using Title Managed Storage, a limited amount of Xbox Live server space Microsoft grants its developers. This system allows Monday Night Combat to receive balance tweaks and is also what powers "Teh Internets" levels found in Super Meat Boy.
Microsoft Xbox One