Noxious Walker

This is one of the more unnerving enemies in the game. It's some sort of zombified roach that stands on its hind legs and walks slowly towards your Pikmin, leaving in its wake a trail of poison gas that fades after a few seconds of lingering in the air. Its face is concealed by a structure that looks almost like a gas-mask filter. Could this mean that the creature is vulnerable to its own poisons and needs to filter them as it breathes? Anyhow, these things are easy if you just take them out with White Pikmin. Otherwise, they'll create too much deadly gas for any Pikmin to deal with.

WARNING
The gas emitted by Noxious Walkers is a highly volatile compound. If an explosion of any kind goes off in the midst of one of their gas clouds, all clouds in the area will violently burst into a massive storm of fire, setting all the Noxious Walkers ablaze. As they run around, their health will deplete until they burn to a crisp and disintegrate, and enemies caught up in the inferno could be instantly killed or at least take a large amount of damage. However, your non-Red Pikmin will be at risk of intense heat, and if the force of the firestorm knocks your Captains down, you may not have time enough to save them from the fire.