Eat other cells
Agar.io is probably the most well known we have on our io games list. The objective in this game is to be the biggest cell in the whole map. In order to achieve this you can do two things: First, you can recollect small balls that lay around the map. Or secondly, you can eat cells that are smaller than you. Remember to be careful with the green viruses, if you are bigger than them and you happen to run over them, your cell will split in many small ones. This may result in a massive loss of mass.