At the heart of our game, Kids vs Zombies, is the conflict between young heroes and zombie adults. We couldn’t create a classic conflict between those two, since zombies right off the bat, seem weak and unattractive for the player, nor could we see PvP based on the conflict of heroes.
Therefore, we decided to create a nonlinear PvP model. Zombies have become mobs, and kids have become playable characters. As a result, the following damage model was formed for the battle: the players (you and your rivals) attack the zombie mobs, and they, in turn, go after the players. The winner is the one who collects the most loot from the zombies.
This model resembles classic PvE and the limitations of player interation. We decided to explore the idea of nonlinear PvP through a system of perks: unique abilities that allow you to either send your rival into the hands of mobs or prevent them from collecting loot, but do not cause direct damage.
So, to attack mobs, players use weapons, and among themselves they only use perks. There is infinite ammo, but the "overheating" mechanics are in place. Magazines are full and constantly reloading if they are about to run out. In the case of perks, the traditional cooldown mechanics are used, so players have to wait some time before they can use any kind of perks again.
How to teach a player?
The nonlinear PvP system is extremely rare, and in this sense, Kids vs Zombies has almost no analogs. When our game went into beta, it became clear that players needed training on how to use perks and how to take advantage of them.
According to available data, we saw that players who managed to use four or more perks show RR1 ~80% higher than those who didn’t use them. That meant that the mechanics worked and caught on. But there was a problem -— those who didn’t manage to learn how to use simply left! We began to solve this problem one step at a time.
The first step was to add a loading tutorial screen to the game. The tutorial animation showed how to use perks and what their benefits are. Unfortunately, it didn't prove to be useful at all! Users used perks once and forgot about them in the battles to come. Take a look at version 933 in the graph below.
Secondly, we fine-tuned the gameplay: the first and most direct solution is to increase the number of enemies in battle. As a result, zombies began to eat players who have been affected by perks more often, and for the users themselves, this mechanic became a more visible part of the battle. The result was slight growth, visible in version 1090 on the chart.
We continued to tweak the mechanics: now the zombies would aggro on players who have been affected by the perk. The cooldown time of the perks has decreased. Perks became more dangerous, and they could be used more often. And that’s when we saw the higher spike — version 1102.
Finally, we went back to working on the user interface and added a "revenge screen" in the lower-left corner. The purpose of the screen is to rouse the players’ emotions: first, trapped players received a custom animation of a specific character who threw a perk, taunting them. Secondly, the loser could now not only see who *perk’ed* them but also see all the bonuses (precious donuts!) they got for doing that. It set the mood and was very much in the style of our universe! As a result, the growth in the number of perks used was modest compared to the previous version. Look at the chart above — 1106.
Our final conclusion was this: interface, art and narrative solutions are important but secondary. The main tool for communicating with the player is the actual gameplay. And the best way to learn game mechanics is to play the game itself.
We’ll continue to experiment and develop the nonlinear PvP model for Kids vs Zombies, with the beta version currently available on Android.