Plants vs. Zombies is a tower defense video game developed and originally published by PopCap Games for Microsoft Windows and Mac OS X systems. The game involves a homeowner using many varieties of plants to repel an army of zombies. The homeowner, along with a neighbor called Crazy Dave, must defend the homeowner's house during day or night, in the front yard and the backyard (including the swimming pool), and even on the roof.
Plants vs. Zombies sees players placing different types of plants and fungi, such as Potato Mines, Pea shooters, Cattails, Hypno-shrooms, Cabbage-pults, Melon-pults, planterns and many others, each with their own unique offensive or defensive capabilities, across the front lawn, back lawn, and roof of a house in order to stop a horde of zombies from devouring the brains of the residents. The playing field is divided into a number of horizontal tracks, and in general, although there are exceptions (such as when the garlic plant is used), a zombie will only move towards the player's house along one track, and most plants can only attack or defend against zombies in the track they are planted in. In the game's initial levels, if the zombie reaches the player's house, a one-shot tool (a lawn mower or pool cleaner) can be used to completely wipe out zombies in that track, but the tool will not be restored until the next level. In later levels, players have to purchase upgrades so as to adapt their lawn-mower to new environments like pools or rooftops. Zombies, except in special cases, will start to devour any plant in their way before continuing towards the house.
The player starts with a limited number of seed packs and seed pack slots that they can use during most levels. New seed packs are gained by completing levels, while the number of slots can be increased through purchases with in-game money. At the start of a level, the player is shown the various types of zombies to expect and given the opportunity to select which seed packs to take into the level. In order to plant a seed, the player must have collected a specific amount of sunlight. Sunlight is generated by plants which provide sunlight at regular intervals, or is automatically generated regularly for the player during daytime levels. Seed packs also have a short time delay before the same seed can be planted again. Several plants are nocturnal, like mushrooms, having a lower sunlight cost and are ideal for nighttime levels, but will remain asleep during daytime levels unless startled by a coffee bean. In the "backyard" levels that includes a swimming pool, seeds must be planted atop lily pads on water spaces (with a few exceptions, such as the spikeweed that cannot be planted on lily pads), while on the roof levels, all seeds must be planted in flower pots. The various plant abilities range from firing projectiles at zombies, turning zombies against each other, quickly exploding and wiping out an area of zombies, and slowing down zombies. Certain plants are highly effective against specific types of zombies, such as a magnet-shroom that can remove metallic items from a zombie, such as helmets and ladders.
The zombies also come in a number of types that have different attributes, in particular, speed, damage tolerance, and abilities. As the player progresses in the game, the zombies will include those wearing makeshift armor, those that are able to jump or fly over plants, and even a disco zombie that is able to summon more zombies from the ground. In each level, zombies will approach the house randomly except at special points where the player will be inundated with a "huge wave" of zombies; a meter on screen shows an approximate timeline for the level so the player can prepare for these waves.
