What does it take to really implement meaningful co-op in your game? A Virus Named Tom developer Tim Keenan delves into the thorny issue -- discussing the challenges and triumphs of building in the mode for his indie game.

About a Virus...

I love playing cooperative games with family and friends. So when I set out to make A Virus Named Tom, I always knew that I would add cooperative play. What I didn't know was how deep the rabbit hole went.

A Virus Named Tom is an action-puzzler where you reconfigure circuits to spread a virus while trying to avoid anti-virus drones. You do this to cause absolute mayhem in a Jetsons-esque future utopia. Your creator, you see, is a bit miffed about being fired after creating said future utopia.

There's a single player campaign, a cooperative campaign (with up to four players), and a vs. mode. Here, I'll talk a bit about what I went through getting the co-op campaign up and running.

It Takes a Village to Destroy a City

"Puzzles aren't cooperative." That's what I was told. You don't see teams of people solving Rubik's Cubes, and you don't see a cooperative mode in Braid (this was also before Portal 2). Cooperation was for killing terrorists, aliens, and zombies.

Solving a complex puzzle is a solitary thing which requires concentration. Cooperation would just be annoying, adding a hindrance. I was also told puzzle games don't need stories. I decided mine was going to have both, because it's my damn game, and that's pretty much the beauty of being an indie dev.

A city infected... by co-op!

Four-player... Just Add Three Players?

Starting a cooperative puzzle game is easy. Just add more players! The first decisions in A Virus Named Tom were the easy ones. I didn't want splitscreen, or to deal with a shared camera, so the entire circuit would have to sit on a single screen. The circuit has four corners, so each player could start in a nice safe place, off the grid. I think somewhere in the recesses of my brain I thought that I could somehow pull a fast one -- that I could just add three players and say "look, if you want, there's co-op play!"

1, 2, 3, 4 players... Must be co-op!

Initially, I tried to ignore the nagging reminders that it wasn't going to be that easy. Sure, the single player levels were fun for co-op, but some levels that would be great for co-op wouldn't work for single player, and vice versa. Trying to design levels that worked well for one to four players wasn't easy.

It also bothered me that the entire co-op campaign could be defeated with a single player, while players two to four sat idly by. I told myself this was a "feature", because players of different skills could play together without the tension, but this felt hollow as time went on. I wanted players to need each other and affect one another, thereby creating a stronger connection.

The final straw was when I decided to go back to targeting a more core audience. The game started as a core game, targeting gamers that would enjoy a challenge in both puzzle and dexterity. As time went on, and the casual marketplace opened up, I got scarred and started making decisions that would be inclusive of as many player types as possible, therefore skewing more casual-friendly.

Eventually, this just didn't feel right. I knew how I originally intended the game to be played, and didn't want to alter that experience, so I abandoned the casual slant and returned to my original core target demographic. This removed my need to support players of very disparate abilities and required at least two of the players to be fairly core players.