Agar.io is a king-of-the-hill style game set in virtual petri dishes. You play as a cell and the aim of the game is to consume as many other cells as possible to grow as large as you can.
I first played Agar.io in mid 2015. I think I was introduced to it by my brother who was playing it one day, and he and my friends all started to play together. We would co-ordinate over Skype and enter a room and try to dominate the leaderboards.
Agar.io is a very simple game and there are only two keyboard commands to learn. You play the role of a small circular cell, and the playing field is filled with little dots that can be consumed to make yourself larger. There are also spiky sun-like objects that threaten to break you apart if you bump into them (although not if you're really small, in which case you can use them to hide inside). Players can chase each other down and attempt to absorb one another, which can be done if your cell is sufficiently larger than the one you are trying to consume. When you do, its mass will be added to yours (a quantitative value for your size is recorded in the screen corner).
It's fun being king of the hill
The fun part of course was the PvP aspect of the game which pitted you against everyone else in the room in a battle to be the largest cell. The leaderboard in the top right corner makes you painfully aware of what rank you are and who is at number one.
It's common to see the whales of the field slowly lumbering about, exerting their massive presence on everyone else around them. They consume dots like no tomorrow and are lethal even when split in two. It actually becomes a bit difficult to survive with such size because the spiky stars get in the way and limit your movement. You run the risk of being split by them and becoming vulnerable to other cells, particularly those who are smaller than you but still on the top 5 slots of the leaderboard, and who are out for blood and often will follow you around waiting for you to mess up.
Agar.io can be exceedingly frustrating when it wants to be, because its easy for collusion to take place. Players can gang up on you and it was often to see players with team tags, clearly indicating that they were working together. It was common to see medium-sized cells share their mass with larger ones or outright sacrifice themselves to make their comrades larger, which put you at a disadvantage, especially if you were on your own. Multiple cells were capable of herding you around the map, forcing you to go in directions that you know will lead you to a massive whale lurking in the distance. If you're quick and lucky, you can make a break for it and sneak out from right beneath them, and when you succeed, it feels so good and fuels you to keep playing even after you've been eaten.