This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / The Nightmare Before Christmas
"Jack's Lament." One can really sympathize with Jack's boredom that's begun to turn into despair
Sally: Jack... I know how you feel.
Jack's moment of despair when Sally uses the fog juice to try and stop him. It's a small reminder of just how happy the prospect of having his own Christmas had made him.
Jack: (heartbroken) There go all of my hopes, my precious plans, my glorious dreams!
While it's played for dark laughs, it's rather heartbreaking to imagine being one of those children, who've presumably been good all year, who eagerly embrace their long-awaited presents only to be attacked by them immediately after.
Jack's cry of "Merry Christmas to all, and to all a good night!" as he plummets down to earth in flames from being shot from the sky.
The denizens of Halloweentown weeping at the supposed death of their beloved leader. The Wolf Man gives a Howl of Sorrow while tears run down his cheeks, and the Mayor tearfully drives through town announcing Jack's death on his car's loudspeaker. And then just to make it even sadder, it's intercut with the policeman driving through town, announcing that Christmas is canceled this year.