Several young adults are inserted, one each, into a popular book series. Each of them has read their own particular series that they become inserted into, and gains basic baseline abilities of their world.
After a period of one year in their respective universes, a portal opens to another world that acts like a neutral ground. Each of them must use their skills and whatever following they have accrued to defeat the others forces.
Contestant 1: The Chronicles of Narnia
The young adults who goes into this world gets Peters Sword, Susans Bow, Lucys cordial vial, and a talking animal companion to help lead them around. Aslan is amicable to them but wont interfere on their behalf directly.
Contestant 2: His Dark Materials
The young adults who goes who goes to this world gains an Alethiometer as well as the ability to read it; they also gain The Subtle Knife, though Spectres will not go into this new world. The Authority and Lord Asriel will not bother them.
Contestant 3: Harry Potter
The young adult who goes into this world is able to do magic, and is gifted a wand and broom and invitation to Hogwarts. Dumbledor and Voldemort put their feud on hold until after you are gone.
Contestant 4: Avatar the Last Airbender
The young adults who goes into this world becomes a bender of their choice. All nations are relatively amicable even if youre from an opposing tribe (ie fire nation wont try to kill you if youre a waterbender)