This is part 2 of my exploration of the systems in Plants vs. Zombies (you can read part one here). In this portion we will explore how PopCap expands upon the systems they introduced in the first level, and how these changes introduce tensions that make the game interesting.
As a cheat-sheet for last time, here are the basic variables we identified as being the design elements in Plants vs. Zombies.
- Defending house on left.
- Zombies attack from right.
- Suns fall on the play-field. Click on them for currency.
- Sun can be spent on plants. Purchasing has cool-down.
- Plants defend your house.
- Zombies attack your house.
In the second level two things are added right away: two additional strips of grass are added around the strip from level 1-1, and you are given a second plant-type – the sunflower. So already, the game's systems are being affected on multiple fronts.
- Change: The play-field has increased in size. The most apparent change is that now there are more options where to place plants. However, this also means there are more lanes that zombies can come down to attack your house.
- Tension: In the early game, make sure that you have sufficient defenses for each lane so one lane isn't weak and gets killed when several zombies spawn in it.
Suns fall on the play-field. Click on them for currency.
- Change: Now, instead of sun only being available at intervals after falling from the sky, the player has agency in the rate at which suns are produced by using sunflowers.
- Tension: The player now has to make a decision whether or not they feel safe enough to increase their sun-production. If they invest too heavily in sunflowers at the beginning of the game, they won't have the proper defenses to fend off the zombies. But if not enough sunflowers are planted, the player's sun-production will be too low later in the game to buy the necessary defenses.
Sun can be spent on plants. Purchasing has cool-down.
- Change: The user now has two options for which plant to purchase - the peashooter or the sunflower. These two plants have different costs.
- Tension: The biggest tension here is the tension of saving vs. spending. Sunflowers are 50 sun cheaper than peashooters, so the player learns to resist wanting to spend all their money. The player has to wait until they have the money to buy the peashooter, or else they won't be able to beat the level.
At this point, the systems reach a level of complexity where the player must begin forming certain strategical heuristics. Here are some of the basic ones I formulated:
- Don't build a peashooter in a lane until a zombie shows up there. Misplacing an early peashooter can spell trouble if a zombie shows up in an unprotected lane
- Keep building sunflowers while I have money in the bank for a peashooter. I know this is relatively safe since I always have the money for reinforcements
- Once you have money for more than two peashooters, keep building peashooters continuously. In the case of a final wave, the cool-down on building peashooters really limits how quickly you can build up defenses. Better to guess ahead of time and defend all lanes rather than scramble against the planting cool-down during a big wave.
I continued playing and took notes on the system changes as the first world progresses, noting new plant, zombie, and gameplay types.
- Plant: Cherry Bomb
- Zombie: Cone Zombie
- Notes: Cone zombie takes much more damage than a typical zombie, forcing the player to use the new Cherry Bomb, where it otherwise might have been ignored.
- Plant: Wall-Nut
- Modifications: Full 5 lanes of grass
- Notes: The additional two lanes of grass add so much complexity in terms of potential placement and points of attack that they don't add any new zombie points. They do add a plant that allows you to block zombies and slow them, probably as an easy patch-up for feeling initially overwhelmed on this full level.
- Modifications: Completely different gameplay type! Wall-Nuts come from a conveyer belt on the top of the screen and the player drops them on the play-field. From there they barrel to the right and hit zombies, basically as an extremely simple bowling game. Almost stupidly simple, but is such a change of pace that it probably keeps the player much more interested. Instead of just getting bored of every new level including one new plant and zombie type and slowly building the complexity, they keep attention by having the player learn something completely new.
- Plant: Potato Mine
- Zombie: Pole-Vaulting Zombie
- Notes: The pole-vaulting zombie is a tricky guy. He moves quickly until he runs into a plant, at which point he vaults over it. This could easily kill you if you didn't know that's the behavior. However, the designers counteract this by giving you a new plant type that is explicitly a mine. What does this mean? The player will probably place the mine in front of all their other plants, causing the pole-vaulting zombie to vault early. Without this, the player could easily lose the level because they didn't know the zombie's behavior. However, with this synergy between the new defense and offense offered in the level the player feels smart for discovering the enemy behavior on their own.
- Plant: Snow Pea
- Zombie: Huge wave
- Notes: What do you do when throwing the first huge waves of enemies at the player? Give them a plant that shoots ice peas that slow down the enemy.
- Plant: Chomper
- Zombie: Bucket-head Zombie
- Modifications: Have so many plants that the player must choose a subset for that level.
- Notes: Another beautiful strong enemy and counter to that enemy being provided in the same level. The bucket-head zombie takes a lot of hits and is likely to get to your plant line, but if you put a Chomper in the front, it can eat it in one bite.
- Plant: Repeater (shoots two peas at a time)
- Notes: This is the level where there aren't any new zombies, but it can be seen as a sort of "review" level where all elements from the previous levels are combined.
- Notes: In the final level of the world they bring back the alternate gameplay type from the fifth level. However, this time they also give you all the plants that you have access to, instead of making it a simple bowling mini-game. This means they remove the economic tension, and make gameplay purely about plant-placement with a tetris-like tension about what the next plant down the conveyor belt will be.
So overall the designers follow a pattern of introducing something new each level. Here are some of the design mantras I gleaned from this:
- Always give the player something new every level. No one wants to play the same game level over and over. However, this doesn't mean that review levels aren't fun and interesting.
- If there is potential gameplay that is very different, but parallel to your main design, use it as a chance to mix things up.
- If you don't force the user to use new tools and systems, you run the risk that they never use them at all. Create gameplay that causes the player to fail unless they use the new items or systems you give them. Do it immediately too, so the player doesn't have to go back later when they start failing to figure out how everything at their disposal that they never use works.
- Recognize the different systemic tensions in your game, and use different levels to accentuate or remove those tensions. Tensions can become exhausting if there is no reprieve.
- When introducing complex new systems, don't be afraid to remove a lot of the complexity that you have built up to teach the player. Bring back the complexity once they understand the essence of the complex new systems. (I actually gleaned this from the first level of the second world, which uses only the most basic zombies to teach you how night works, but it was too interesting not to include).
That concludes my look at the design of Plants vs. Zombies. The game continues to grow in interesting ways as the game progresses, but I had to set a scope on this dive somewhere. I'd love to hear what you think, so reach out to me on twitter.