I have taken megacities (Cities with at least 10 million residents), and made so you have to guess the cities at least 2x larger! So can you name all the cities with at least 20 million residents?
Another good quiz Devvik! I have nominated! One suggestion is to add this to the start of the description: "We have taken mega cities and increased the criteria by twofold." In my personal opinion, it blends perfectly into the next part of your description.