Well actually when I went into the mission I think you can get the thagomizers because I was able to skip the portal and get behind the door killing the night wardens I'm not sure what to do at that point afterwards but its a clue there's something else of this mission why would this mission be the daily heroic with a boss who has the thagomizers this has to be the only mission to obtain it so before you people start saying this is BS you should try running in the mission and experimenting in it before giving up