* Just entered the Legendary section of the Legendary Underworld (so all replacements will be legendary)
* Entire team of four was Epic creatures, and those were the last of my Epics (barely made it!)
* Lost all my creatures in one turn (hourglass expired + lost all HP)
Failed the Underworld, must restart chamber. (No crash. Amusingly enough, it said I "ran out of creatures" and displayed the dozen Legendaries I hadn't fielded yet.)
Also, the game actually let me pick the first legendary replacement (for expired hourglass) before declaring that I lost.
I pick my replacement Legendaries, life goes on in the Underworld.
I've never had this issue before, but I've also never lost the last of my (group A) creatures at the same time while in the (group
part of the Underworld.