"Ariel, a sixteen-year-old mermaid princess, is dissatisfied with life under the sea and curious about the human world" would read better as something like "A sixteen-year-old mermaid princess named Ariel is unhappy with underwater life and curious about human life on land"
"travel to the ocean surface to watch a celebration for the birthday of Prince Eric on a ship, with whom Ariel falls in love"..... how about just "travel to the ocean surface to watch Prince Eric celebrate his birthday" and "Ariel falls in love with Eric"?
"the unconscious Eric" → "an unconscious Eric"
"Despite her claims that she's doing this"..... avoid contractions unless part of a quote or title
"out of the kindness of her heart"..... a bit lengthy, let's go with simply "out of kindness"
"disguises herself as a beautiful young woman"..... the "beautiful" bit seems POV
Not sure everyone reading this will automatically known what a "polyp" in "Triton transforms into a polyp" is supposed to mean, try a different word Never mind on this one
"Eric kills Ursula by running her through the abdomen with the ship's splintered bowsprit" is somewhat wordy, try "Eric stabs and kills Ursula with the ship's splintered bowsprit".
Cast
Is there any particular reason detail is given on Ariel and no other characters? Either expand on the other characters or remove the extended detail for her.
Only the voices for Ariel and "additional voices" are supported citations. The rest need to be cited.
Production
Story development
"but was put on hold due to various circumstances" → "but was delayed due to various circumstances"
"Walt Disney Studios chairman" isn't needed as it has already been established that Katzenberg was CEO
"approved of" would be a term for "greenlit"
Per WP:OVERITE, refs doesn't need to be used twice in a row in the third paragraph, take out the instance after "sea witch" where ref#11 is used, and ref#12 should just be used at the end of the paragraph
Animation
More WP:OVERCITE- ref#13 should only be used at the end of "paint support to Mermaid" in first paragraph, ref#9 shouldn't be used after the bit on Alyssa Milano, ref#17 should just be used after the "replaced by Carroll" bit, ref#9 should just be used once at the end of the fourth paragraph, and only once at the end of the fifth paragraph
Music
Even more WP:OVERCITE- ref#16 should just be used at the end of the paragraph
I'd add another paragraph's worth of information to this subsection- one paragraph alone seems imbalanced with the other subsections of "Production". Actually, on second thought the link to its soundtrack will do.
Release
Home media
"home video releases in May 1990, eight months after the release of the film"..... if this film was released November 1989, than this should say six months
Reception
Box office
Remove ref#2 after the "additional gross" bit per WP:OVERCITE