The Mysterious Life-Form (Mysterious Life Form in Europe, 謎の生命体?, lit.: "Life Form of Mystery") is the name given to one of the forms of the Plasm Wraith. In this form, it looks like a blob of plasm. It follows Brittany, or whoever is guiding the Pikmin carrying Captain Olimar, through the labyrinth that is the Formidable Oak. Once Olimar is outside, the creature reverts to the Plasm Wraith.
Pikmin 3 Prima Guide
“Before the Plasm Wraith reveals its true self, it appears as the Mysterious Life-Form. This giant, slow-moving creature uses its amorphous body to absorb its victims. It's best to simply avoid the Mysterious Life-Form. However, if a battle is unavoidable, wait for the creature to turn an opaque gold color before you attack. When the creature is translucent, attacking Pikmin will simply be absorbed by the Mysterious Life-Form.”
When first spotted atop the oak, the Plasm Wraith transforms into a Goolix-like creature called the Mysterious Life-Form, and envelopes Olimar in order to protect him, but is defeated with Pikmin attacks. With no other way to go, the group issues the Pikmin to carry Olimar through the oak itself. For reasons not currently explained, the Pikmin are unable to find the path they must take, and instead, it is decided that they follow after Brittany. As soon as they enter, the Mysterious Life-Form drops from the cave ceiling and begins chasing the player down the chasm. The player must stay ahead of it while overcoming the various obstacles present within the oak in order to safely escape.
The point of the confrontation with the Mysterious Life-Form is not to destroy it, but to escape from it. There are a few notes that you should consider...
After you successfully escape the chasm, you will appear in an arena outside. The Mysterious Life-Form eventually reaches the exit as well, and upon doing so, will revert to its original humanoid shape and inhale all of its scattered plasm, growing to an immense size. It will then inhale and secure Olimar inside its body, thus commencing the final battle.
Because the explorers do not know about this form of the Plasm Wraith, they simply nickname it "Mysterious Life-Form". In Europe, it's spelled as "Mysterious Life Form". In Japan, it uses the same name, 謎の生命体?, which translates to "Life Form of Mystery". Internally, it is called
Names in other languages