In most cases, no. American fiction is focused on the main narrative and doesn't commonly incorporate post-credit scenes. However, there might be some rare exceptions in experimental or unconventional works.
A post - credit scene scary story might involve a cursed object. In the main movie, the object seems harmless, but in the post - credit, it starts to glow and strange noises come from it. It then causes chaos in the empty theater where it was left. Also, there could be a post - credit scene where a character finds a diary that tells of a horrible past. As they read it, shadowy figures start to appear around them, and the words in the diary start to bleed, creating a truly terrifying moment.
The back story of Carnage and Venom is quite complex. Both originated from the symbiote species. Venom was the first to bond with a human host, and Carnage emerged as a more violent and unstable offshoot.
In the comics, the outcome of their battles varies. Sometimes Venom emerges victorious and kills Carnage, but there are also instances where Carnage escapes or the fight ends inconclusively.