The fog levels are the fourth stage of the Adventure Mode section of Plants vs. Zombies. They take place in the backyard of the player's house, but during the night. Also, in each level, up to two-thirds of the lawn is covered in fog (the fog-covered area expands as the player progresses through the stage), in which both plants and zombies are very difficult to see. During the final wave (every wave in Survival), Ducky Tube Zombies and their variants surface from random points in the four-by-two rectangle of the pool farthest from the player's house. During Level 4-10, a conveyor-belt level, a storm rolls in, making the screen pitch black between the flashes of lightning illuminating the yard. Along with the Adventure Mode levels, there are four mini-games that take place in the fog: It's Raining Seeds, Dark Stormy Night, Air Raid and Invisi-ghoul.
Because of the fog mechanic, certain plants obtained on these levels have the ability to clear them out. For example, the Plantern was added to illuminate part of the fog. Players can use the Torchwood for this as well, but it has a smaller range. The Blover was introduced to temporarily blow away the fog and Balloon Zombies. The Split Pea and Starfruit were introduced to counter Digger Zombies. Plants also added in the Fog stage are the Sea-shroom (the aquatic equivalent to the Puff-shroom), Cactus, Pumpkin, and Magnet-shroom. Also, after obtaining the taco in Level 4-4, Crazy Dave's Twiddydinkies gains the Gloom-shroom and Cattail for the player to purchase.
While playing Adventure Mode for the second time, the Zombie Yeti will appear during Level 4-10. If defeated before it runs away, the Zombie Yeti will drop five diamonds and then will be randomly encountered in other levels. When it is encountered in other levels, it will drop four diamonds when killed.
The song played during this stage is called "Rigor Mormist," which is very likely to be a portmanteau of "Rigor mortis" and "mist."
All mini-games taking place in the night backyard play the track "Rigor Mormist" except for Dark Stormy Night with no music.
The fog in the music video is made by a fog machine. However, it covers the bottom half of the lawn instead of the right half.
There are only eight levels that actually take place in Fog, as Level 4-5 consists of Vasebreaker levels (which looks just like a Night level), and Level 4-10 is a stormy night. It makes sense because in Vasebreaker, it is important to be able to see what the player is breaking. Also, there is usually no fog when there is a storm (though fog may signal an incoming storm and thus it leads to the events of Level 4-10).
Turning the volume on can be important in the Fog levels so the player can tell which zombies are coming when he or she cannot see them.
For Level 4-1 and PC Air Raid, the fog covers three columns of the screen, for Levels 4-2 to 4-6 (except 4-5), the fog covers four columns, for the rest of the Fog stage, it covers five columns, and for 4-10, Invisi-ghoul and Dark Stormy Night, it does not appear. Other fog stages not listed have the same amount of fog as stage 4-6. In the early iPhone versions, fog covers one more column than the other versions.
The player can see zombies slightly in the fog. This doesn't apply that much if the player does not have 3D acceleration enabled. This also does not apply to the Nintendo DS and Nintendo DSiWare versions, as the fog is thick enough on these versions that seeing through it without plant aid is nearly impossible. There are tiny gaps in the fog clouds in these versions, though.
While the Night stage has two inconveniences (lack of sun, graves), Pool has two (ambush zombies, water), and Roof has three (roof angle, inability to plant without Flower Pots, Bungee Zombies that drop zombies), Fog levels have four (lack of sun, water, fog, and ambush zombies).
On the Nintendo DS, Nintendo DSiWare, and PC versions, the player can see a zombie's head at the very top when it is in the top lane.
There is a glitch on 4-10 for the Nintendo DS and Nintendo DSiWare versions where the player can see a highlighted version of the plant held by the stylus before planting it while the screen is pitch black.
4-10 and the hidden PC mini-game Dark Stormy Night are not the same and have completely different sets of plants coming out. One example is that the mini-game has Peashooters, but 4-10 does not.
Inside an update to the Android version, the Fog on Fog levels goes back to only half of the backyard but is much denser. Before, the Fog on some levels could cover all but two or three columns. This also applied to the earliest iPhone version of Poolis unknown why the lights inside the player's house do not light up the backyard. It is possible that the storm may have caused a blackout.
4-10 and Dark Stormy Night are the only official levels that do not have background music.
This stage allows the player to plant most plants in the game, excluding Grave Buster and Coffee Bean.
This And Pool, has six lanes rather than five lanes.