- For the Plants vs Zombies 2 version, see 20 Below Zero (PvZ2).
Usually, the best stages to obtain this achievement are within Night stages, however, it is do-able on other stages. It is easiest to get in Last Stand if the player stalls the zombies using Tall-nuts or Wall-nuts. It is also easily obtainable in Survival: Endless due to the sheer amount of zombies that appear.
One way to do this is in Survival: Endless. Build a good strategy that can reach over ten flags. When there is another small wave coming, use the Ice-shroom to freeze the zombies because it can freeze some zombies that are not on the screen yet.
If you do not have Survival unlocked and you do not want to wait, you can probably unlock this on the final wave of the last Night level. Alternatively, try to wait for a while until there are enough zombies on the lawn before planting the Ice-shroom.
Another strategy would be playing a Night level, and putting defensive plants in every row until the zombies count up to twenty. It is obviously a good idea to bring some plants to help deal with the zombies afterwards.
Another way to beat this achievement is to go to the mini-game Last Stand and put several columns of Tall-nuts and Pumpkins out and after 20 zombies walk out, use the Ice-shroom, or just simply stall the zombies until there is 20 of them and use the Ice-shroom. Do not put the nuts in the last column because they are easier to count if you do not do this.
- Coffee Bean
- Ice-shroom, the main component
- Doom-shroom, for some serious field clearing
- Anything else.
Go through the level as you normally would, planting Sunflowers and Peashooters. At the final wave, use the shovel to clear your entire lawn, plant an Ice-shroom near the back of your lawn, and wait for the zombies to populate the lawn (there will be about 20). Once all the zombies populate the lawn, wake up the Ice-shroom and let it do its work. After that, you can plant a Doom-shroom in the middle of the lawn, and then wake it up to clear the field and complete the level. If necessary, keep your Sunflowers in case you have to some emergency planting.
A very simple way to get this achievement is surviving to the last flag of Last Stand. A lot of zombies appear, giving you the perfect opportunity to plant an Ice-shroom and wake it up. That is, if you have enough sun saved up.
When you play Invisi-ghoul, try to use Ice-shroom on the final wave. Make sure you plant it at the correct time, or you will freeze none of the final-wave zombies.
- This is the only achievement in Plants vs. Zombies to have its first word as a number.
- In Plants vs. Zombies 2, there is an achievement with the same name.
- In addition, it has nearly the same objective.