In the above mentioned link to Agar.io clone the copyright infringing part is the "agar.io," not the actual reproduction of the game. The game play it self can

In the above mentioned link to Agar.io clone the copyright infringing part is the "agar.io," not the actual reproduction of the game. The game play it self can not be copyrighted, and it can not be patented because there have been several prior art games with exact same gameplay (or very similar). There is a very similar planet like game for the iOS that I used to play back in 2010, and that's just off the top of my head. In the main link Agar.io has a very fair DMCA claim if their JS has been literally copied, even if it has than been subsequently altered. However, if one was to make a game like "Bob's Better Floating Balls that Eat Each Other" from scratch, I don't think Agar.io would have a fair claim. I am guessing that they also have a trademark out on Agar.io.