Unlike other platforms that require online authentication, GOG games can be used without an internet connection once downloaded.
The official source currently lists the PC Game Mortal Kombat 1+2+3 for $5.99. Mortal Kombat 1 2 3 Free Download (GOG)
The bundle supports cloud saves and includes easy access to game manuals and sound settings from the launch menu. and new fighters
Added a "Run" button, "Dial-a-Combo" attacks, and new fighters, though it famously excluded Scorpion until later updates. GOG Availability and Features requiring only 512 MB of RAM
These classics are lightweight, requiring only 512 MB of RAM, 2 GB of storage, and a processor of at least 1.8 GHz. Mortal Kombat 1+2+3 - GOG.com