Suneo is showing off his child-sized remote robot toy and hoping to do better, Nobita claims he had one that was bigger than a house like in cartoons and comics. He rushes home to ask Doraemon for help but ends up a big fight where Doraemon runs off into the north pole to "cool off". Nobita follows hoping to find Doraemon. Instead, he finds a blue ball and mistakens it for Doraemon. Suddenly a large object that resembled a robot foot drops next to him. He decides to take it home thinking it was one of Doraemon's gadgets and before long, even more parts drop in and aroudn his home.

After discovering the parts didn't belong to Doraemon, they decide to assemble the parts anyway in a mirror world using one of Doraemon's gadgets so that it wouldn't bother anyone. Soon, a girl named Riruru appears to claim the robot back and they soon learn there will soon be a robot invasion.

Actually watched the 2011 remake before this original movie (now available in remastered HD) so that I could see how different it was and it's pretty good. Always been a fan of the movies where the gang ends up in some other world supported by Doraemon's gadgets or where they have to fight off the enemy like this. The remake is mostly the same only this has a darker tone to it whereas the remake uses brighter colours and cuter character expressions. They added a mascot in the remake too whereas here they don't.

Other differences in the original they probably changed because the scenes might have been bad influence for kids:

Also just noticed how much the Nobi home has changed since the 1980s where the old sliding doors has been replaced by modern day Western style, swing open doors.

Still worth a watch if you prefer a darker version of the remake.