This series of gamebooks uses a system similar to that of the Advanced Dungeons & Dragons Adventure Gamebooks, which isn't surprising, since it's also a spin-off of a TSR role-playing game. In each volume, the reader controls one or more characters from Marvel comics. Each character comes with a set of pre-defined attributes which are combined with dice rolls and compared with target numbers in order to perform actions. Characters also have Health Points (which are self-explanatory) and Karma Points (which change as a result of good or bad deeds and which may be spent to improve dice rolls). The books were first published in the United States by TSR and then several were reprinted in a different order by Puffin in the UK.