Are dead sessions always a Time challenge? Caliborn's was, and alt-Calliope says hers was the same, but those are kind of the same session so maybe that's not a general pattern? I could see them being a random Aspect, unwinnable by any player of a different Aspect. The minions would be related to that Aspect too in some way.

Seems like they’re a time trial- Not a Time trial, just a time trial. It’s designed to be unwinnable by design, but being a Time Player, and specially a Lord of Time, seems to have favored Caliborn to do the impossible. Dead Sessions aren’t a challenge, or a trial. They’re a punishment. In fact, I headcanon that even if you win a Dead session, you’d remain stuck in it, unable to leave it, just. Alone, forever, unconditional immortality not letting you die. It’s not meant to be fun or challenging, it’s just unfair. Buuuut he got the express way through Juju Succ, the lucky bastard.