YU-NO/YMMV

Idiot Plot: Ayumi's route.
Inferred Holocaust: Ayumi’s route strongly implies that Mio was trapped beneath Triangle Mountain just like in her own route. By the apparent mechanics of the Reflector and alternate dimensions, this means that Mio probably dies beneath Triangle Mountain in every route apart from her own. But hey, Mio does technically have an escape route so long as she doesn’t give up… right?
That One Puzzle: In Mio's route, underneath Triangle Mountain. You cannot proceed until you solve a somewhat tricky game of picross, which is very difficult for those who haven't solved any of them before. This is not made easier by the numbers being represented by made-up symbols instead.