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As others have noted, you have to avoid names. You can't use their world or some specific monsters (no illithids!). Other monsters, like gnolls and orcs, predate D&D and thus are fair game (so ...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/48712 License name: CC BY-SA 4.0 License URL: https://creativecommons.org/licenses/by-sa/4.0/
#2: Initial revision
As others have noted, you have to avoid names. You can't use their world or some specific monsters (no illithids!). Other monsters, like gnolls and orcs, predate D&D and thus are fair game (so to speak). I think the rise of LitRPG shows that plenty of people want to read about game-like worlds, at least as long as you put an interesting twist on it. In my my own series (Sword of the Bright Lady, published by Pyr) experience points are tangible objects, like coins that you can collect and trade. This change lets me write about a fantasy world that is like the ones we play in rather than like the ones that usually get described in stories. My characters talk about being a fourth level wizard and my high ranking warriors can jump off of cliffs without dying. Yet it's not a parody or a game; it's a serious epic (albeit with plenty of humor, as to be expected when a Earth-borne mechanical engineer encounters magic for the first time). The real problem with writing your game as a novel is that the plot that makes for an exciting game rarely makes for an exciting story, and vice versa. In a game, the players derive satisfaction from their own actions; but in a story, the action of the characters exist to satisfy the reader. One notable exception: The TV show The Expanse is derived from an RPG run by its two authors (there are a couple of places in the books where this is obvious). But clearly they've cut and trimmed the campaign to meet their dramatic needs.