This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Tanz der Vampire
The song "Stärker als wir sind" is extremely touching for some. They get teary even just thinking about listening to it, or pondering the lyrics too much. It may be that the lyrics are so strong and hopeful in the face of darkness, and Sarah's part is soaring and happy.
Rebecca reacting to Chagal's death with a slow, sad reprise of his theme tune, especially when you consider it's the last we see of Rebecca, who up until then has been a minor comic role. Almost everyone else in the play gets something at least roughly approximating a happy ending, and Rebecca exits three quarters through the first act sobbing and alone.
Die unstillbare Gier is a tragic subversion of the "I Want" Song, in which von Krolock tells the story of how becoming close to people he loves will always lead to destruction since he will turn them into vampires.
Für Sarah could count as well, especially when you know what's going to happen next.