- Anyone's death.
- Gregor's final scene with Luxa even more so. Knowing they'll probably never see each other again...
- Gregor's entire situation in the Overland. He's witnessed more pointless death and killing then any person his age ever should, and given how he's probably never going to return to the Underland he has to spend the rest of his life hiding that from other people.
Tear Jerker / The Underland Chronicles