Marina sings a dark reprise of her song on the night of her death.
The ending to the anime is possibly worse than the short story. Right after Marina jumps into the sea, the Prince remembers her... but it's too late. Fritz is left to tearfully chase the sea foam that was Marina.
Made even worse when, as an adult, you realize that outside of a Disney universe, what Triton did qualifies as straight-up emotional abuse. Destroying your child's property, even in anger, has the potential to scar them for life. It doesn't help that it easily allowed Flotsam and Jetsam to take advantage of her either.
Sebastian's grief over the whole thing, as he indirectly caused the incident when he accidentally blurted out Ariel's secret.
Sebastian: Ariel, I—
Ariel:Just go away.
Even Triton seems to have realized what he has done was too far witnessing her sobbing. His face after seeing what he's done and broken her heart is awful.
When Ursula wages a deal with Triton to hand the kingdom over to her to get Ariel back. Seeing how his own actions caused this chain of events, he sadly hangs his head down and willingly signs the contract.
Ariel excitedly running down stairs, only to see Eric being romantic with "Vanessa".
In a strange sort of way, Ursula mourning the loss of her minions and the Mama Bear-fueled rampage she commits afterward.
The ending, where everyone has made up and all is well as a Triumphant Reprise of "Part of Your World" sung, though this is more of a case of happy tears.
"I love you, Daddy."
Return to the Sea
Ariel finding out Melody ran away.
This scene from the beginning.
Ariel: This is the only way. Melody can't know anything about merpeople or Atlantica...or even you, Daddy.
The image of Melody being changed back into a human while in the cave and nearly drowning as a result.
Melody being humiliated at her birthday party, calling herself the princess of disaster, and when she hears the guests talking meanly about her. Poor girl.
Triton watching the death of his beloved queen in a pirate attack, followed by him throwing away the music box far into the sea (which Sebastian secretly witnessed).
Sebastian getting arrested.
Triton lying down all sad with a statue of him and Athena in the background.
Ariel does the exact same thing in her room, and decides to slip out as a piano version of the music box tune plays.
Ariel finding the music box and remembering her mother.
Sebastian: When your mother died, the whole kingdom was heartbroken. The heart that never healed... was your father's.
Ariel: It's so sad... He's forgotten what it's like to be happy.
The TV Series
The character of Gabriela being based on a real deaf girl who was a fan of the show and died during the first season.