They should have called both games MK ULTRA because they're torture. Not sure how far I'll be getting with either of these but I sure won't be finishing either.
That's right, it's the infamous side-games where you play as specific characters, fleshing out their story a bit. I think they were planning a whole series of these, but the idea bombed out quickly and only really got revisited with the Liu Kang / Kung Lao driven Shaolin Monks years and years later. That game is actually good, probably because Ed Boon took command on it unlike these two disasters.
In said disasters you're playing as Sub-Zero and Jax respectively. Special Forces was supposed to also center around Sonya, which would have added a lot to the game (and let them knock out another character from their no doubt long list of side games they'd have to do if this "do a game starring each character" madness continued). After some development hell, playable Sonya was left out of the game. Originally you chose one of the two characters at the outset and played as them throughout, with the second character appearing to offer assists or show up in cutscenes. Well, far as I can tell Sonya was totally removed.
I don't know how many characters they were planning to do games for, but it appears that it was at least the original cast. Mythologies: Sub-Zero has the titular character and Scorpion, while Special Forces was supposed to star Jax and Sonya going aganst Kano. That leaves Raiden and Liu Kang, who were...the next planned games. However they also had a Baraka game on the drawing board so they may have extended into MK2's roster. The Baraka and Liu Kang games were cancelled, while the concepts for the Raiden game were retooled into aforementioned "only good spinoff" Shaolin Monks with Liu Kang and Kung Lao. (Edit: I forgot Johnny Cage lol...but so did they)
Fun Fact: While both are prequels to the main series, Special Forces is canonically the first game in the entire MK-verse, taking place before any of the others.