When Spider-Man accepted the Other, he was reborn with all new powers and a second chance at life. In order to do so, he had to accept the spider side of being Spider-Man, and the spider-god with it. He returned... but what if he didn't? What if he rejected the Other, and fought against it?
Thanks to What If? Spider-Man The Other, fans know the answer. And it's a horror story that ends with the return of Peter Parker's first and true love, Gwen Stacy. And since she is dead, this story is as grotesque as you think.
On a world similar to Earth-616, Peter Parker was dying from cellular degeneration. The Spider-Verse supervillain Morlun took advantage of Spider-Man in his weakened state and nearly killed him in battle, going as far as to even eat his eye. In their final fight, Peter kills Morlun, but Peter seemingly dies of his own wounds shortly after. But death is not always what it seems. Peter is confronted by his Other, the spider-essence -- which had a simple offer for him: be reborn, but fully accepting his spider side. While Peter of Earth-616 accepted the offer, an alternate universe Peter rejects it, killing the Great Weaver instead. So Peter's body remains in a cocoon, as his spirit accepts his fate, he slowly begins to die.
That is, of course, until the Venom symbiote senses Peter's state. As the first human Venom ever bonded with, there is a special and strong connection between the two. Even though Venom was currently bonded with Mac Gargon, the symbiote jumped at the chance to connect with Peter once again. With Peter's metamorphosis stalled, he is half a man, and the symbiote intended to fill in the gap to make him whole. What occurs over the following months is the slow degradation of Peter Parker, both physically and mentally -- until finally he loses the fight and succumbs to the symbiote. The resulting creature is not Peter nor Venom, but something in between: Poison.
Poison's first stop is Avengers Tower, where he means to share himself with Mary Jane so they can be together again, by "replicating himself within her." Mary Jane rejects his offer, saying she would rather be dead. Poison admits that wouldn't actually be an issue for his symbiote abilities, but the former lovers are then interrupted by the rest of the Avengers. Poison takes the opportunity to snarkily accuse Wolverine and Mary Jane of a romance, but Mary Jane ends the fight by agreeing to go with him, so he would stop hurting the others. But she also promises she will make every one of the days they are together a living hell for what Poison has done to her and Peter. And with a crack of thunder, Poison disappears... determined to find a new mate.
The Mary Jane heartbreak shows that Poison needs someone who would be pliable, and supportive -- someone he could rebuild in his own image. Or someone who is simply not equipped to refuse him. As Poison said to MJ, his mate doesn't need to be alive to fill the role, and let the Venom symbiote replicate itself to bring her to life. And you never forget your first true love.
The issue ends with Poison traveling to Forest Hills Cemetery, with the uncovered grave of Gwen Stacy paired with the monster's own narration. The final panels make it clear that Poison has dug up the corpse of Gwen, and placed her inside a cocoon of her own. Of course, Venom can't replicate itself to bring the dead back to life, instead it needs to produce an offspring -- fully revealed as a hand emerges from the cocoon covered in the red tendrils of Venom's spawn, Carnage. Fans are left to imagine the resurrected Carnage-Gwen and her reunion with what remains of Spider-Man, which is likely for the best.