Plasm Wraith

The Plasm Wraith is the final boss in Pikmin 3, and is responsible for capturing Captain Olimar. It is a virtually-featureless, vaguely-humanoid Waterwraith-like being made entirely out of a cellular protoplasmic mass, which allows it to split different parts of its body off to create other semi-independent entities.

The Plasm Wraith is encountered at the Formidable Oak, having taken Olimar captive with what appears to be curiosity rather than maliciousness. Efforts to rescue Olimar cause the being to become the Mysterious Life Form and slowly ooze towards Olimar, attempting to retake him, until he reaches the outside of the oak. Once this occurs the Plasm Wraith takes its golden humanoid form, locks Olimar in its core, and begins to attack.

As with all final bosses, the path leading up to it, and/or the boss fight itself, requires the knowledge and utilization of every single Pikmin type.

In Fanon Games
In Pikmin Ultimate, it acts as a mini-boss of the cave, Ghoul's resting place. It is substantially easier than in Pikmin 3, as it has less hit points, and has lost it's elemental plasm attacks. However, is stabbing attack is more longer, and he is faster from the original. He can also become the Mysterious Life Form for a brief moment of time. Other than the speed, the more dangerous stabbing attack and the transform, the fight is technically the same.