4th of the I, Zombie Mania. This is actually easy, as the name suggests.
Peashooter Sunflower Snow Pea Wall Nut Fume Shroom Zombie (50) Buckethead (125) Ladder Zombie (150) At first, have a ladder Zombie plant a ladder on the row with NO Fume-Shrooms and 2+ Sunflowers. Next, clear the row with a Buckethead. Do the same for other rows without worrying about Fumes. However, do not clear rows with Fume-Shrooms using Ladders, as it passes through the Ladder. Use the Bucketheads for that. As for Snow Peas, consider using Ladders as they are not affected by the slow-down.