I apologize if the reply is late, but it was the Spartan trainees, and to an extent, both Daisy's and Ralph's sanities. Ralph broke down crying in front of Daisy when he confessed he nearly killed his clone, and Daisy herself turned desperate and nearly killed her own clone to claim her life back. At the end of the episode, it mentions the two other trainees killed themselves.

The episode does elaborate incredibly well on this, and it was one of those podcasts that disturbed me more than I should while I'm working (... Dan Carlin's Hardcore History episode about the horrors of WWI trench warfare and mud being one of those things).

It's a similar theme to a tabletop roleplaying game called Changeling: The Lost. Your character is a human that got snatched by a lovecraftian abomination, replaced with another clone that is meant to live your entire life as if you hadn't vanished, and tortured physically and psychologically, to be turned into a literal monster... which, somehow, is among the handful that gets to escape the hold of their sadistic owners, only to realize somebody else, -you-, continued to live your life, as if you had never left.

Same job, same family, same actions, same hobbies, same circles, everything the same.

You, however, are forever changed.

"You meet a mirror image of yourself! Someone that kept living your life. I mean, they probably seemed to be more you... than you!"