I, Zombie (formatted as i, Zombie in some versions) is a series of Puzzle Mode levels, in which the player "plants" zombies with sun to destroy cardboard plants and get to the brains at the end of each row. A level is completed when all of the brains have been eaten, but if the player runs out of sun before all the brains are eaten, they will lose. The last level, I, Zombie Endless, is an endless mode. After every three streaks of I, Zombie Endless, a present containing a Zen Garden plant, a chocolate, a money bag with gold coins, or a diamond will drop.
"I, Zombie" is a reference to the book and film I, Robot.
It can also be based on the quote "I Frankenstein."
I, Zombie is a very strategic puzzle game. First, you must find ways of getting the brains whether by using Gargantuars to smash them, or other zombies to eat them. Additionally, sun must be collected first by also having zombies eat Sunflowers or Bungee Zombies stealing them. You must have a good understanding of the abilities of both plants and zombies. For example, if a row has only two or three cardboard Peashooters, it is safe to say that sending out a Buckethead Zombie or a Football Zombie will earn you a brain and further them to completing the level. You cannot take back zombies once they are placed, so you must plan wisely according to the cost of each zombie and the amount of sun left. Each Sunflower eaten will give 200 sun.
There are ten levels of I, Zombie, which get harder in succession. All of the levels take place in the equivalent of the Night stage of the game, presumably so that the player can only get sun from getting rid of Sunflowers and for the mushrooms to stay awake.
In this mode zombies cost sun while in Versus Mode they cost brains.
At the beginning of the first level, Crazy Dave tells the player that the zombies want to practice invading houses. Since he did not want any plants harmed, he put cardboard plants on the player's lawn.
Sunflower is the only plant that appears in every level of I, Zombie. This is because she is needed to produce sun in order to place the zombies in these levels.
The writing is also spelled incorrectly to make it look like the zombies wrote it.
In the level Me Smash!, Gargantuars smash the brains (and a squashed brain sprite appears on the ground) instead of eating them, since they only crush plants.
I, Zombie is the only game in Puzzle Mode that does not return in Plants vs. Zombies 2 (excluding the Chinese version of the game).
Dancing Zombie is the highest costing zombie in this mode, even surpassing Gargantuar.
Gargantuars can still throw their Imps in I, Zombie, but this does not usually happen; as the Gargantuars are only capable of throwing their Imps if they are less than halfway across the lawn, and the line marking where zombies can be placed is approximately halfway across the lawn
Unless there is Squash next to the line, this may cause the Gargantuar to throw his Imp. In which case if the closest plant to the brain in the same lane are Sunflowers or Spikeweed, the Imp may eat the brain.
The code "dance" makes the zombies move somewhat faster than usual, so typing "dance" until the player sees the zombies go at their speed limit is a partial advantage.
I, Zombie is not available in the Nintendo DSiWare version of Plants vs. Zombies.
Doing an I, Zombie level without mushrooms (like the first one) will get you the No Fungus Among Us achievement, except in the iOS version of Plants vs. Zombies.
On the Nintendo DS version of Plants vs. Zombies, the plants do not look like cardboard and if the player uses Action Replay to give plants rapid fire, the plants are affected.
In the iPhone and iPod versions, the first level is free but the other eight and endless are purchased through Crazy Dave's Twiddydinkies for 150,000 coins.
If the player places a Pole Vaulting Zombie in a lane where there are no plants, just a brain, he will lose his pole immediately.
This also happens with Balloon Zombie; the balloon will pop when it reaches the brain and the zombie eats it.
If the player can click or tap fast, they can make multiple Bungee Zombies grab the same Sunflower, as for a while after taken, the Sunflower is still on the lawn while the first Bungee Zombie is raised. This does not work on the iPhone version, as only one Bungee Zombie can target a space at any given time.
In the Nintendo DS version of Plants vs. Zombies, most zombie's seed packets only shows the head, except for the Imp's seed packet, as its seed packet shows its head and part of its body, and the Conehead Zombie's seed packet, which only shows the roadcone.
In the Nintendo DS version of Plants vs. Zombies, when choosing where to plant an Imp, the Imp can be seen with a bone sticking out.
In the iPhone, iPod, Xbox Live Arcade, PlayStation Network, and PlayStation Vita versions of Plants vs. Zombies, after nearly reaching the player's house, the zombies suddenly disappear.