We're going to look at merging the "Too Individual" and "Too plot based" close reasons into "Too Story Based". Keeping in mind the discussions from Risk Factor definition: Too Individual/Character Based and Are Too Character Based and Too Plot Based the same? here is the proposed close reason.
Close reason: Story-based
You are asking questions about a story set in a world instead of about building a world.
Asking about plot elements such as the actions of characters, rather than about the world in which your story takes place, is off-topic on Worldbuilding. Capabilities of characters within a world and creation of groups of characters (like nations) are on-topic, but questions must focus on what is possible or likely to develop, not what someone would or should do.
Questions about the back story of a character are also prone to fall into being Too Story Based. Checking whether a specific element of a back story that you have already written is possible or likely then that is likely to be on topic however "write this for me" is not. You should also be careful to explain why the back story is relevant to the world and building that world, rather than being just development of that character.
How to Fix:
Rephrase the question to remove all references to individual actions and any "should" or "would" parts of the question.
"Would Joe Marine 17 climb this hill wearing his backpack" is off-topic. "Could a well-trained marine wearing a 30kg weight backpack complete a 1-mile route with 500' of ascent in 10 minutes" is on-topic.
"Would government pass such-and-such law" is off-topic. "What could cause government to pass such-and-such law given these societal conditions" is on-topic.
Be careful when doing this not to make the question too broad, it should still be specific and answerable.
Only the person who is writing a story can decide how characters will act or plots will develop. Worldbuilding can determine what is possible, but the choices about what happens given those possibilities belong to the author.
Points for discussion
Should filling in gaps in knowledge be acceptable questions (for example bullet from orbit). The consensus seems to be that it should so long as the question is answerable but this might be worth further debate.
The question asks "how can Joe take over the world" not, "in which world could Joe take over". The question asks for the actions of the characters, who isn't, by his function, a significant figure of the World.
Questions asking about capability are on topic, questions about whether a specific person would or should use that capability are off topic.
A lot of people seem to think that Facebook vs Cthulhu is off topic but not really giving any reasons for why. Does it fall under this close reason. If so why?
Satan Santa: Question is not about helping refine the backstory of a historical figure, it says 'make one for me'. That is clearly story/plot, not about the impact they have had on the world. We made an exception for historical figures of importance to allow questions about how they shaped a world, not so that we could do all the work for a plot/story suggestions.
Satan Santa: The connection between the backstory requested in the question and the world being built is too tenuous (thus its 'worlbuilding-ness" isn't clear enough).
NPCs in Video Game: This one seems quite clearly agreed. The question asks about the reaction of a group of characters. Does not influence the world as it is built.
I think if we can clarify these discussion points then we will be able to create a general community wiki Q&A for "Why has my question been closed as Too Story Based and how do I fix it" and then create a custom close reason with a link to that Q&A. We should try and make the guidelines as clear as possible within that question as to what is and is not off topic as too story based.