I just discovered this game... Read All Plague Inc. is a strategy-simulation game in which the player controls a plague which has infected patient zero. The player can choose between various game-modes, plagues and viruses, and complete the objective set by the game-mode by evolving the plague and adapting to various environments. The objectives include, but are not limited to: Infecting and killing the world's population with a pathogen, enslaving the world's population with the "Neurax Worm" or converting the world's population into zombies with the "Necroa Virus". However, there is a time pressure to complete the game before humans, the opponent, develop a cure for the plague.
I just discovered this game (it came out in 2012 originally) and have been really enjoying it! Basically you start off with a disease (depending on the level you're playing it could be a bacteria, a virus, a fungus or many other pathogens, each with different abilities) and you control how it evolves to infect and kill the entire human population.
You have three different areas to evolve the disease in: Transmission - How the disease infects people (could be spread by animals or blood or just in the air or water), Symptoms - How the disease affects people (starting with minor symptoms like coughing or rashes, working up to total organ failure) and Abilities - How the disease fights to stay alive (ability to survive in extreme climates and drug resistance to name some ways)
As your disease progresses, humans will notice it. If you develop your symptoms too early, the humans might find a cure before you have time to spread to everyone. But some symptoms also help spread the disease quicker, so it's a fun balancing act to find creative ways to kill everyone off.
In addition to the standard play modes, there are really unique scenarios. I played one called Santa's Little Helper. Here's the synopsis in game: The world is dark and gloomy. Boring governments worldwide have banned holidays, laughter and celebrations. Humanity has forgotten how to have fun - people dress in grey and spend all their time working. Luckily, the Neurax Worm has teamed up with Santa and is determined to infect the whole world with joy and happiness. In this scenario, you try to infect everyone with a brain controlling parasite that causes them to be happy. If people get too happy, the government notices and tries to find a cure. You can send planes full of "presents" from infected countries to uninfected countries to spread the parasite faster.
Other scenarios I've played have included a resurgence of the Black Death and the Simian Flu (from the new Planet of the Apes movies). In the Simian Flu, not only are you mutating the virus to spread and kill humans, but you also can work to increase ape intelligence and lethality. Unfortunately the Simian Flu scenario was just a sampling. I'll have to buy the various scenario expansion packs eventually.
I don't normally spend money on mobile games, but this is one I think I will. There's so much variety in play on this, I think I can get a lot of bang for my buck.
I definitely recommend checking this game out if you haven't yet!