Fumes

Fumes are a purple cloud of spores produced by Fume-shrooms and Gloom-shrooms. Each cloud of Fumes does one Pea of damage, but hits everything within it, i.e. everything that the fume-producing plant can shoot at the time, making it an Area of Effect attack. Gloom-shrooms fire four times faster than the Fume-shroom, and as fast as a Gatling Pea. The Fume-shroom hits the four spaces in front of it, while the Gloom-shroom hits all eight squares around it.

Fumes are renowned for their ability to pass through shields, namely Screen Doors, Newspapers, Ladders and Trash Cans. While Lobbed-shot Plants can also circumvent shields, Fumes, unlike Lobbed-shot Plants, also damage the shields, making them slightly more effective given the same damage per second if there are non-fume and non-Lobbed-shot Plants as well as the shield will be destroyed faster, and if the zombie is not already dead, these other plants will be able to contribute against the zombie.

Trivia

 * The Fume-shroom and Gloom-shroom's Fumes look like multiple Spores.
 * Fumes, following to the dictionary, are toxic vapors, explaining why they go through shields. This does not explain their decapitating and shield-damaging effects, however.
 * It is odd that even though Fume-shrooms hit zombies in their torso, the headwear of various zombies can still block it.
 * Maybe it's because the zombies can't inhale the fumes due to headwear like Buckethead Zombie's.
 * Fumes are the only non-lobbed projectiles that ignore the roof's angle.
 * The Fume-shroom attacks all zombies in its range, damaging all zombies that are touched by the spores.
 * Fumes are the only Area of Effect projectiles that do equal damage to all zombies in range.
 * It is unknown how fumes do damage, as zombies don't breathe.
 * It is possible that the fumes are corrosive, along with being toxic.
 * This can also explain the damage to the shields.