I would have Poison...
Sure it's a rendition of Venom, but an awesome and relentless one. The Venom symbiote detaches from Peter (like everyone knows) then rejoins with him, but Peter doesn't try to fight it off this time (it's a "What If..." comic called What If...?: Spider-Man: The Other) he just lets it consume him.
After some time, and after Peter is officially dead inside, the symbiote renames itself to Poison...