The Backyardigans meet The Little Mermaid

The Backyardigans meet The Little Mermaid is an upcoming Nick Jr./Disney crossover to be made by Hiatt Grey.

Plot
Ariel is a 16-year-old mermaid princess in the kingdom of Atlantica, a fantasy kingdom in the Atlantic Ocean. She is fascinated by the human world above. With her best friend Flounder, Ariel collects human artifacts in her grotto and often goes to the surface of the ocean to visit Scuttle, a seagull who offers very inaccurate knowledge of human culture. She ignores the warnings of her father King Triton, the ruler of Atlantica, and Sebastian, a crab who serves as Triton's adviser and court composer, that contact between merpeople and humans is forbidden.

One night, Ariel, Flounder, and an unwilling Sebastian travel to the ocean surface to watch a celebration for Prince Eric's birthday on a ship. Ariel instantly falls in love with Eric. Shortly afterward, a violent storm arrives, which wrecks the ship and tosses Eric overboard. Ariel rescues him and brings him to shore. She sings to him, but immediately leaves just as he regains consciousness to avoid being discovered. Fascinated by the memory of her voice, Eric vows to find the girl who saved and sang to him, and Ariel vows to find a way to join him in his world. Noticing a change in Ariel's behavior, Triton questions Sebastian about her behavior and learns of her love for Eric. Triton confronts Ariel in her grotto, and destroys the artifacts she collected with his trident. After Triton leaves, two eels named Flotsam and Jetsam convince Ariel to visit Ursula the sea witch.

Ursula makes a deal with Ariel to transform her into a human for three days in exchange for Ariel's voice, which Ursula puts in a nautilus shell. Within these three days, Ariel must receive the "kiss of true love" from Eric. If Ariel gets Eric to kiss her, she will remain a human permanently. Otherwise, she will transform back into a mermaid and belong to Ursula. Ariel accepts and is then given human legs and taken to the surface by Flounder and Sebastian. Eric finds Ariel on the beach and takes her to his castle, unaware that she is the one who had rescued him earlier. Ariel spends time with Eric, and at the end of the second day, they almost kiss but are thwarted by Flotsam and Jetsam. Angered at Ariel's close success, Ursula disguises herself as a beautiful young woman named Vanessa and appears onshore singing with Ariel's voice. Eric recognizes the song and, in her disguise, Ursula casts a hypnotic enchantment on Eric to make him forget about Ariel.

The next day, Ariel discovers that Eric will be married to Vanessa. Scuttle discovers Vanessa's true identity and informs Ariel, who immediately pursues the wedding barge. Sebastian informs Triton, and Scuttle disrupts the wedding with the help of various sea animals. In the chaos, the nautilus shell around Ursula's neck is destroyed, restoring Ariel's voice and breaking Ursula's enchantment over Eric. Realizing that Ariel is the girl who saved his life, Eric rushes to kiss her, but the sun sets and Ariel transforms back into a mermaid. Ursula then reveals herself and kidnaps Ariel. Triton confronts Ursula and demands Ariel's release, but the deal is inviolable. At Ursula's urging, Triton agrees to take Ariel's place as Ursula's prisoner, giving up his trident. Ariel is released as Triton transforms into a polyp and loses his authority over Atlantica. Ursula declares herself the new ruler, but before she can use the trident, while Ariel confronts Ursula, Eric intervenes with a harpoon and hurts Ursula. Ursula attempts to destroy Eric, but Ariel intervenes, causing Ursula to inadvertently kill Flotsam and Jetsam. Enraged, Ursula uses the trident to grow to a monstrous size.

Ariel and Eric reunite on the surface just before Ursula grows past and towers over them. She then gains full control of the entire ocean, creating a storm and bringing sunken ships to the surface. Just as Ursula is about to destroy Ariel, Eric steers a wrecked ship towards Ursula, impaling her with its splintered bowsprit killing her. With Ursula dead, Triton and the other polyps in Ursula's garden revert to their original forms. Realizing that Ariel truly loves Eric, Triton willingly changes her from a mermaid into a human permanently and approves her marriage to Eric. Ariel and Eric marry on a ship and depart.