Underwater City is the ??? world in Plants vs. Zombies 2. The world is based on Atlantis City. The world takes place in 1950s.
The main gimmick in this world is water, which all land plants (except Guacodile) will die after a period of time unless an Oxygen Algae is planted.
The second gimmick introduced in Day 5 is darkness. The lawn starts to be bright, but it will dark over time until the lawn is completely dark. Any plant can be used to illuminate, but on its own tile only (using Sea Pickle is recommended to light up areas). There is also a new power-up exclusive to this area that illuminates the whole lawn for 30 seconds.
The third gimmick that introduced in Part 2 is Conduit Tile. Any plant that planted on Conduit Tile will have their level increased by 5 for 20 seconds (example: a lvl 1 Peashooter when planted on Conduit Tile will become lvl 6 Peashooter.)
Another gimmick is all Fila-mint and Winter-mint Family plants will receive a boost throughout all Underwater City levels and fire plants are completely useless in this world.
Make your way through these water-ridden depths where the light is low and the zombies are plentiful! Use your Oxygen Algaes and Sea Pickles to let your plants survive so that they can throw these zombies to the shore!
There are a total of 31 levels and 1 boss battle to play in Underwater City, as well as introducing ??? new plants (one of which returns from a previous game) and ??? new zombies (??? of which returns from a previous game).
*Prizes that are not money bags are unlocked only first time.
- Oxygen Algae: Creates a 3x3 oxygen around it for land plants. Obtained after completing Day 1.
- Sea Pickle: Illuminates in 3x3 area. Can be stacked to increase illumination range. Obtained after completing Day 5.
- Seashooter: Seashooters shoot watery peas at zombies and unleash a stream of water every 15th attack. Obtained after completing Day 11.
- Dried Kelp: Dried Kelp quickly shoots piercing seaweed at zombies, however, when planted above water, Dried Kelp will now become dry, giving it a bit more health, and will shoot slower, more heavy damaging seaweed bits. Obtained after completing Day 17.
- Bubbleberry: Creates bubbles that can send zombies back tiles. Lighter zombies go farther than heavier ones. Obtained after completing Day 23.
- Lily of the Jelly: Possesses the zombie encounters it into allies. Possessed zombies can be reverted if it gets killed. Obtained after completing Day 27.
- Seads: Seads boosts aquatic plants in a 3x3 area around it and transforms into an aquatic plant after a while. This is Part 1's premium plant.
- Cropedo: Cropedos fire a limited amount of torpedoes that deal huge damage. It gains more torpedoes when planted near aquatic plants. This is Part 2's premium plant.
- Deep Sea Diver: Swims slowly, ignoring plants. When it comes close to a Oxygen Algae or a Sea Pickle, it will crash itself towards in it, killing itself and that plant. First seen on Day 2.
- Clamshell Zombie: Has a huge amount of health, however, when eating a plant, allows lobbing plants to deal damage to it directly. First seen on Day 4.
- Submarine Zombie: Submarine Zombie moves slowly and will sometimes shoot torpedoes at plants, dealing heavy damage and pushing every zombie in front of it farther. Lights up the area in front of it. First seen on Day 9.
- Trident Zombie: Throws a trident when encounters a plant in front him four tiles, in which the trident can instant kill the plant it hits and acts as a blocker. First seen on Day 17.
- Squid Rider Imp: Moves quickly across the lane. The squid also creates black ink that makes tiles harder to see without a Sea Pickle. First seen on Day 21.
- Zombie Dolphin: Zombie Dolphin, when touching a Conduit Tile, will kill the plant on it and spawn 4 zombies of varying difficulty. First seen on Day 28.
- Zombot Volt-Krakenator: TBA
- This world is a collaboration between Boston Pineapple and Asterplant.
- There are several Minecraft references in this world.
- Sea Pickle is a reference to Sea Pickle from Minecraft.
- Trench Gargantuar and Cropedo are references to Drowned.
- Conduit Tile is inspired by Conduit.
- Trident Zombie is a reference to Trident weapon.