Acidwraith

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

Strategy
When encountered, the beast falls from the sky and moves around on its stone 'rollers'. It will chase Olimar and any Pikmin nearby, with greater focus on crushing the active Captain. It is invincible to any Pikmin assault, even if petrified, except that of Purple Pikmin. When a Purple Pikmin lands on or near the Acidwraith in a fashion that would stun any other beast, it turns a deep shade of black. This will instantly kill the Purple Pikmin though. Thankfully, a new Candypop Bud species, the Dual Bud will combine two Pikmin together for a limited time. Once the time expires, it will split back into the original two Pikmin. A Purple Pikmin and a Green Pikmin will need to be combined to kill this beast. Like this, it is vulnerable to Green Pikmin attacks (it will asphyxiate any other Pikmin that attempt to attack it). When the Wraith's health has been fully depleted, the rollers crumble and the Acidwraith will scoot all around the cave, dissolving any Pikmin it walks through. Attack with more Purple-Greens and then you can easily attack it with Green Pikmin. When defeated, it will vanish into nothing.

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

Pikmin: Invasion of the Giants
This beast appears only once in this game and on the final level of the Acidic Complex. It is noticeably weaker than the Water Wraith, as Green Pikmin can damage it. This is likely due to the fact that any other Pikmin will be instantly killed when touching it, and you couldn't bring any other Pikmin over anyway. When you knock it off the rollers, it will run around and drop pools of acid.