This movie was dubbed in English by Speedy Video Malaysia as Doraemon - Nobita Tetsujinheiden.
Doraemon's Long Tales VOL.7 Noby vs. the Mecha Army
Noby builds a gigantic robot from random parts he found at the North Pole. Thinking of the robot as a cool toy, he is having fun with it in the mirror world with Doraemon and Shizuka when they realize that the robot is actually not a toy, but a deadly weapon that can destroy buildings with a single blow. The three promise to keep this a secret, but Noby lets it slip when he meets Lyril, a mysterious girl who is looking for a robot. Noby then discovers the terrifying truth: Lyril has taken over the mirror world, building a secret base with plans to invade Earth! The Mecha Army could arrive at any moment to destroy cities and enslave humans. Can Noby and his gang stop them? A story of love, courage and friendship, the seventh tale of the Doraemon's Long Tales series!
The story begins with Nobita and Shizuka sitting on the pipes in the yard they hang out at while Suneo showed off his robot. Nobita grew jealous and asked Doraemon to build him a giant robot. Coincidently, robot parts began to fall from the sky. Then Nobita and Doraemon began to assemble the robot. As soon as they finished, Nobita, Doraemon, and Shizuka realized that the robot (Zanda Clause) was a war machine in an incident. After that Nobita met a girl name Riruru, she told Nobita that the robot was her's. Nobita gave her the robot and the entrance to mirror world. Doraemon and Nobita followed Riruru and recognized that she was a spy from Metropolis and built a base to welcome the army.