Acidwraith

The Acidwraith may be the ectoplasmic incarnation of a kind of psychic phenomenon, much like the Waterwraith. It has an acidic, translucent body and its appearance is generally humanoid in shape, with the suggestion of a head, body, arms, and legs, but without distinct characteristics. The Acidwraith's name is a combination of acid, given its acidic appearance, and wraith, which means ghost or phantom.

Strategy
When initially encountered, the beast falls from above and moves around on its stone rollers. It will chase leaders and any Pikmin nearby, with a greater focus on crushing the active leader. It is invincible to any Pikmin assault, even while petrified, except by that of a special Pikmin type known as Purple-Green Pikmin, which are created by throwing Purple Pikmin and Green Pikmin into a Dual Bud. The Purple-Green Pikmin can not only stun the creature and render it vulnerable but survive touching it as well. When the Acidwraith is stunned, its body will turn black and it will hunch down over its rollers. When the Acidwraith's health has been fully depleted, the rollers crumble and the creature will scuttle around the entire area, dissolving any Pikmin it walks through. When defeated, it will vanish.

In Pikmin: The After Years
In Pikmin: The After Years, this enemy will drop two random colored 20-pellets and one 10-pellet.

In Pikmin: Invasion of the Giants
The Acidwraith appears only once in this game and on the final level of the Acidic Complex. It is noticeably weaker than the Waterwraith, as Green Pikmin can damage it. This is likely due to how any other Pikmin will be instantly killed when touching it, and how other Pikmin colors cannot be brought into the cave. When it is knocked it off its rollers, it will run around and produce pools of acid.

Olimar's notes

 * "A most curious phenomenon of nature. It has no life, and yet responds to many actions in ways that exhibit conscious thought. Viewers are instantly overcome with fear at the sight of it... A most curious phenomenon..."

Louie's notes

 * "Absolutely nothing is left when this monster is defeated. If you were to take a chunk while it was still alive, you still wouldn't get anything but stone rollers or acid."

The President's notes

 * "Stow any non-Green Pikmin away somewhere safe. The best technique is to follow behind with flowered Green Pikmin and repeatedly toss Pikmin onto it. When it is off the rollers, pursue and freeze it with ultra-bitter spray, then attack. Use the ultra-bitter spray when it is rolling and spray your Pikmin with ultra-spicy spray for best results."