Scout.
WYR be killed by Aslan (Jadis) or Rilian (LotGK)?
Killed by Rilian most definitely.
WYR turn into an enhanced version of yourself (like Strawberry-to-Fledge) or into something else entirely (like Eustace-to-dragon)?
Eustace to dragon
WYR ride on a unicorn or a centaur?
Unicorn.
WYR run from your uncle or from (possibly well-meaning, but you can't be sure) Animals?
Uncle, I think.
WYR go to Narnia or Charn?
Narnia! 😀
WYR travel from Calormen to Archenland or from Narnia to the Underworlds?
Archenland.
WYR go to Calormen or Ettinsmoor?
Calormen, methinks.
WYR deal with Green Mist or Jadis?
Well, the mist doesn't kill, and Jadis does, so mist.
WYR meet Gael or Gwendolen?
Gwendolen. She actually exists. (*still resents the character of Gael and her presence on the Dawn Treader*)
WYR be led into battle by Oreius or Glenstorm?
Orieus.
WYR attack Miraz's castle or defend Anvard?
Defend Anvard. I'm a proven defensive fighter. And besides, that fight is canonical. 😉
WYR kidnap the heir to the throne or raise said heir unknowingly?
Raise the heir unknowingly
WYR meet Cor or Corin?
Cor
WYR try to box with Corin or spar with Cor?
Spar with Cor.
WYR get to know King Frank or King Lune?
