Doraemon Movie 08: Nobita to Ryuu no Kishi  

Doraemon the Movie: Nobita and the Knights on Dinosaurs, 映画 ドラえもん のび太と竜の騎士, Doraemon Movie 8: Nobita to Ryuu no Kishi

In the story, Doraemon constructed a secret base for his friends in an underground cave. However, one of them, Suneo, got lost while exploring the caves. Despite everyone else finding their way back out, Suneo remained missing. After some time had passed, they discovered that the entrance to the caves had been sealed shut. In order to escape, they needed to locate another exit. Eventually, they stumbled upon a dinosaur world and were rescued by Vanho, a soldier. Upon being saved, Vanho revealed that he had found Suneo and was planning on using Doraemon's group as human specimens in order to take over the Earth's surface.