Hot answers tagged formatting
Capitalize it: the Darkness. I believe Tolkien did this with the Ring. It's the common way in fantasy (and christian religion: some god versus God).
Capitalizing it is good, but coming up with another name for it is better. Churchill famously called it the Black Dog. Yours could be the Black Oil, or Dark Oil, or Devil's Touch, et cetera.
For this specific case, I don't see a reason to set it off. In fact, I would likely find emphasis-by-formatting distracting. Here's why I don't think you need to do anything special: You've already mentioned the darkness. You've described it in a vivid, visceral way. Then you immediately refer to it as "this darkness." Readers will know that you're ...
You'd use the character name. Most screenplays are written well before they're cast, so it would be impossible to use the actor name. And even if you knew the actor (like, it was part of a series) you'd use the character name because it's the character saying the line, not the actor. ETA: You can see this, for example, in the screenplay for Empire Strikes ...
Typically, italics indicate when a word is being used in a non-standard manner. This seems to me the best choice for the examples given. I could see capitalizing if it was being anthropomorphized or used as a title ("The Darkness"), but that doesn't seem to be the case here. So you have no choice but to fight alone. Fight this darkness alone. ...
Honestly, I think you're good with whatever style you choose, as long as you're consistent. As far as your options go: Italics. Do not use if you need it for other things that are typically typeset in italics such as biological proper species names. Capitalization. Only disadvantage can be that it comes with a certain level of personification. As in, the ...
I would probably use italics for this. Another option you might want to consider is small caps. It makes words stand out as different, but not painfully so (like all-caps-plus-bold might).
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