Acidwraith

The Acidwraith is a species of supernatura that has a body made of acid.

=In fanon games=

In Pikmin: The After Years
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 but without distinct characteristics. 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 Candypop 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, it hunches down and turns black. When the Acidwraith's health has been fully depleted, the rollers crumble and the creature scuttles about the entire area, dissolving any Pikmin it walks through. When defeated, it will vanish, leaving behind two random colored 20-pellets and one 10-pellet.

In Pikmin: Invasion of the Giants
The Acidwraith appears only once in Pikmin: Invasion of the Giants, 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 its acid body, and how other Pikmin colors can not be brought into the cave. When it is knocked it off its rollers, it runs around and produces pools of acid.