I'm planning to write a book based on a game of Dungeons and Dragons. The rest of the people in my party will get credit as will the DM, who wrote the adventure. If I change the things that were created solely by WotC, such as "Tiefling," and because the idea did not come from one the quest books, would it be considered copyright?
I'm not an expert on copyright law, but I'm fairly sure that there isn't any reason you couldn't write a story based on a D&D campaign. As long as you make sure to change anything that may be specifically owned by Wizards of the Coast (like your example with tieflings) or part of an established cannon(I think the default setting for d&d is the forgotten realms.) An example I would give for something similar to your question would be the webcomic Darken(http://darkencomic.com/) which draws many elements and tropes from D&D and the forgotten realms, but is (to my knowledge) not infringing upon anyone's copyrights.