The Fantastic Four is Marvel's First Family, breaking the glass door for superhero comics from the publisher and becoming one of the most influential comic books ever. However, in Stan Lee's original draft for the heroes, he imagined a different kind of superteam with much darker powers. If the original version of the Fantastic Four had been published instead, it could have changed the trajectory of the Marvel Universe forever.
Stan Lee and Jack Kirby redefined superhero comics following the release of Fantastic Four #1 in 1961. Marvel's first family brought the Marvel Age of Comics to life, with the Fantastic Four ushered in the era that took superheroes in a new, more mature direction. The Fantastic Four starred Reed Richards, Johnny Storm, Ben Grimm, and Sue Storm, all of whom gained incredible powers from cosmic rays during a trip to space. The Fantastic Four's success would lead to the creation of Spider-Man, the Hulk, and the X-Men, as the appetite for superhero comics exploded in the early 60s. However, Lee originally wrote the Fantastic Four much darker than they appeared in their debut issue.
In How Doc Savage Inspired The Fantastic Four by Kirk Kimball, he points to the original plot outline for the Fantastic Four, which teases much darker powers for each hero. For example, Johnny Storm could only use his powers for five minutes at a time before returning back to normal. Would he fall to his death if he was mid-air? Reed Richards could stretch his body into almost any shape, but in doing so, he suffered increasingly unbearable pain that made him weaker the stretchier he became. Sue Storm remained the Invisible Woman but would have been invisible at all times. She would have worn a mask to be seen, as Lee put it, Sue "can not become visible again." Funny enough, the character that was changed the least was Ben Grimm. The Thing was supposed to be much slower, as the Fantastic Four worried he would become out of control and cause harm.
The original outline changed significantly despite Lee's original plans, as its likely co-creator and collaborator Jack Kirby helped steer the Fantastic Four's powers in a brighter direction. Richards suffering pain each time he used his powers, Sue Storm being invisible always, and Johnny not being able to use his powers for an extended period would have had significant impacts on the future Marvel Universe - as if that team had been successful, maybe the subsequent heroes introduced after the FF would have also had much darker tones.
Thankfully, Lee and Kirby's Fantastic Four changed the initial script, and the team's dark powers changed ahead of their debut. However, the Fantastic Four's original powers are Marvel's ultimate What If? as it would have changed the future Marvel Universe in unforeseen, significant ways. Who knows if the publisher would be around today if they'd used Lee's original outline.