I have one player that may be playing Adam Warlock when he gets the chance, so I made an Adam Warlock circa formation of the Guardians of the Galaxy datafile, and then later came up with some milestones for him.
In addition to Adam Warlock, in a move that should not have surprised me at at, +Christopher Osmundson took me up on the "play anyone not available in the event for 20 XP" unlockable, which I was expecting to be used to transport Spider-Man or Deadpool or somebody across the galaxy to participate in the event.
Instead, he switched to playing R'kin, the little Skrull that hung out with Super-Skrull during Annihilation. So I made up a few milestones for him as well. On the WAY outside chance that you have a player that wants to play as that cosmic powerhouse R'kin, you are all set.