No Fungus Among Us

Strategy
This achievement is relatively easy to obtain. It can be beaten by using Sunflowers and Peashooters or Cabbage-pults (Wall-nuts, Potato Mines, and Squash are optional, but very helpful) on level 2-1. It isn't very different from a Day level, so it can be beaten easily with a similar strategy. Cabbage-pults may be a better choice that Peashooters, as they can damage the Newspaper Zombies directly. Just plant a row of Sunflowers in back, a few rows of Peashooters or Cabbage-pults in front of them, and use instant kills as necessary and you should be fine.

Note: Grave Busters and Planterns don't count as mushrooms, so you can use those. You can also earn this achievement by playing Vasebreaker in the Puzzle Mode, simply by not using the seed packets containing mushrooms.

Note: Doing the note listed above doesn't work on Game of the Year edition on PC, as the vases do not contain mushrooms. Doing I, Zombie also counts for the easiest way to get this achievement.

Note: Completing a Fog level without using mushrooms does not unlock this Achievement, plus you can try to get it when you beat the game.