Here’s my set-up for the next film: Dr. Curt Connors, who keeps a piece of the symbiote in Spidey 3 for study, will attempt to regrow his lost arm with a reptilian-derived serum. When his self-experiment goes wrong (as they always do in Spider-world), he changes into the Lizard.
While undergoing his transformation, Connors trashes his lab, freeing the piece of the Venom symbiote. The symbiote escapes the lab and finds a new host. As the new host melds with the black symbiote, it leaves behind a puddle of red goo- the Carnage symbiote, which bonds to a psycho criminal named Cletus Cassidy.
Meanwhile, JJ Jameson has hired Kraven the Hunter to come to NYC and hunt down the Lizard, whom the Bugle has branded “the Alligator in the sewer!” Spidey realizes his friend Connors is the Lizard and fights with Kraven to save him. Kraven brushes aside the Bugle’s publicity stunt to hunt a more “ultimate” prize- Spider-man.
After escaping Kraven, Spidey clashes unexpectedly with Venom. Its new host has no animosity towards Spidey, but warns him to stay out of his way. He doesn’t; Venom and Spidey clash.
Meanwhile, Carnage goes on tear across New York. Venom and Carnage clash in an amazing effects battle of the symbiotes! Kraven catches Lizard while Spidey was busy with Venom. He doesn’t kill him b/c Connors’ wife has made it known her husband is the Lizard. Kraven, still thirsting for a kill gets wind of the Venom/Carnage battle and goes to hunt them down.
Meanwhile, Spidey helps Connors return to human form. Connors and Parker develop the soundwave amplifier to defeat the symbiotes. (Connors taking the role originally played by Reed Richards in the comics when Spidey first fought Venom.)
Spidey and Connors realize Venom is fighting against Carnage, but they use the soundwave amplifier against both men to remove the symbiotes from their hosts. Connors and Spidey return to the lab where-
Kraven, having tracked down Spidey. ambushes Spider-man. Connors frees the Venom symbiote and merges with it to help Spidey fight Kraven. Connors has both arms as the Venom symbiote. They beat Kraven. Spidey uses the soundwave amplifier to separate Connors and the symbiote and all is well again. Until…
Parker returns to Aunt May’s and finds HIS PARENTS waiting for him.
Spidey 5: Chameleon and Spider Slayers (No “clones” stuff, because that was a terrible, terrible idea in the comics. His parents are “spider slayers” in disguise. Chameleon has hired the man who built the Spider Slayers in order to expose Spider-man identity and kill him.)