Here is how Ariel and Eric explained about Melody's disappearance in Genesis Park III.
After the escape, Yuna was upset with Eric.
Princess Yuna: Time for you to explain, Eric.
Prince Eric: Alright, Melody is out there on this island with Max Goof, John Smith and one of your mentors, Cassim and Ford Pines and his brother, Stanley.
Ariel: It's been too long since they've disappeared.
Princess Skyla: No wonder you asked us to guide you here, You needed our help to rescue Melody.
Britney Sweet: Didn't see it coming.
Twilight Sparkle (Human): My friends and I've been on this island.
Princess Yuna: That was when we got lost in. This is Pangea, Where the treasure that our folks found a long time ago, The home of the Tribal Penguins, The only Habitat of the Dinosaurs and other Extinct Animals.
Sunburst (Human): It's true, We've seen it all.
Princess Flurry Heart: Come on, Guys. (looked at Journal 12) According to Journal 12, It could be possible to find the way out.
Twilight Sparkle (Human): Must have been quite an adventure.
Rarity (Human): (looked at her boots and had gone muddy) My boots look awful.
Moon Shoes brings out a shoe polisher, She got the boots clean enough as a whistle.
Moon Shoes: Much better.
Rarity (Human): Thank you, Moon Shoes.
Princess Yuna: Come on, Let's go.
They started exploring the Island finding a way out, Even during a rescue party.
At the plane wreck, Yuna and the others searched for some materials. The Journals started glowing inside of the plane when they found them and their supplies of food.
Princess Yuna: There are the landing gears in the plane, They must be, But knocked out of it.
Princess Skyla: There's wings, They fell off after crashing, The windows are badly broken. And there's engines and propellers, They should be put into some good use somehow.
They took their supplies and parts of the planes with them.
Rainbow Dash (Human): We'll have to work on them.
Nyx: Look! It's a video camera!
Princess Yuna: The batteries are running low, I'll take care of it. (use her magic to make a permanent power source)
Dipper Pines: Great work, Yuna. Now, We'll find out more where Grunkle Stan and Grunke Ford are.
Yuna turns the video, It's got every images on footage.
Melody: (on camera) I'm ready to get down, Max!
Max Goof: (on camera) Alright, One.... Two..... Three! (uncoupled Melody's safety gear) Okey, Here I come!
Melody: (on camera) Alright, Max! Come on! Let's meet up with Ford, Stanley, Cassim and John!
Mabel Pines: Grunkle Stan and Grunkle Ford were on this island.
Pacifica Northwest: Let's hope they're okay.
The camera shows Melody, Max, Ford and Stanley Pines, John Smith and Cassim finding a safe area.
Max Goofy: (on camera) The camera is still on!
Melody: (on camera) We'll be safe here. Let's stop here for a few nights.
Max Goof: (on camera) Good idea.
The camera turns off and Yuna kept it safe in her saddlebag, She realized how Ariel missed her daughter.
Ariel: Melody's out there, I hope she's okay.
Prince Eric: It's going to be alright, Ariel.
Goofy: (in Yuna's mind) Max has been gone with Melody, Ford and Stanley Pines, Cassim and John Smith for a really long time. I hope he's okay.
Princess Yuna: I'll help you find Melody. We're going to find Max, Ford and Stanley Pines, Cassim and John Smith as well.
Spike (Human): And we'll work together on this.
Ariel: Thank you, Yuna.
Sunset Shimmer (Human): Let's move out!
The group took the parasail down. They found Max's cap, It Yuna noticing that Max and Melody were here. They started searching in this jungle and through the falls.