20 Below Zero is an achievement in Plants vs. Zombies 2. It is worth 5 points on Game Center for iOS devices and 500 XP on Google Play Games for Android devices. To earn it, the player has to freeze 20 zombies by feeding an Iceberg Lettuce with Plant Food.
The easiest way to obtain this achievement is to play Ancient Egypt - Day 24. Because this is a Last Stand level that allows the use of Iceberg Lettuce, it will give plenty of time to place multiple defensive plants before any zombies come. Iceberg Lettuces are very cheap with a sun cost of 0, allowing more defensive plants to be placed. Working in columns from left to right, fill as much of the board as you can with Tall-nuts. Allow the level to play out, but be ready to act quickly. Do not panic when the Explorer Zombies start burning the Tall-nuts. Moments before the Explorer Zombies reach the lawn mowers, a large amount of zombies will come onto the screen via sandstorms. Once they have appeared on the board, quickly place an Iceberg Lettuce and freeze every zombie via Plant Food.
Another easy way is to use a boosted Iceberg Lettuce in levels. This will save Plant Food and it will freeze every zombie when it is planted on the lawn.
Another way to earn this achievement is to wait until the final wave of a three or four flag level and then use the Plant Food on the Iceberg Lettuce once they are all on screen. The player can go to Endless Zone and use the same tactic as well.
Avoid using up all of your Plant Food, as it will only make it harder to earn the achievement. However, you may replenish it with the use of Power Lily.
- Its requirement is very similar to the achievement of the same name in the original game, the only difference is that it requires Plant Food and Iceberg Lettuce rather than Ice-shroom.