I had some friends with me for the last Taken champion on Mars and Fear's Embrace. [spoiler]And for the sociopaths who don't like helping people, the echos of Oryx and Taken champions are ultra bosses, so they can drop exotic engrams if you use Three of Coins. Yes, I know the exotic will probably be a duplicate. :([/spoiler]I soloed everything else. The Taken Champion on the Rocket Yard was the toughest. You have to luck out and hope there are 3 other Guardians around. The Summoner's Circle is recommended to have a fireteam because one Guardian has to carry the orb. I just did my best Sam Fisher from Splinter Cell and ran around all the ogres. The end boss surprised me by making chase on the elevated walkways.