Water Bear

The Water Bear is a strange, unique lifeform appearing in Pikmin Z. Its entire body is gelatinous, it having six stubby legs to move around, and a round hole in front of the head.

Biology
The Water Bear is capable of changing its body composition to that of a selection of hazards and dropping pools of said hazard onto the battlefield. It is not known how it does this.
 * Diet: unknown
 * Predators: unknown

Piklopedia entry

 * "Little information I could gather on it. It's just too ... odd. Too unknown to be classified into anything, or truly work out into logic."

Standard form
At the beginning of the fight, the Water Bear moves around the arena in its standard form, which makes it vulnerable to attack. The only method to harm the creature is to get it in its water state. To do that, survive its attacks until it's finished, which it'll turn back to its standard state while it's recharging. Throw Rock Pikmin at it, and it'll slide off the platform and into the water, turning it into its water state. Use Blue Pikmin to get at the core until it forces them out of it.
 * Its fire form covers the beast in a coat of lava, with flames shooting out of its back. It does shake occasionally, which causes fire to fall all over the arena.
 * Its electric form turns its body yellow, with static lightning shooting out in many directions. It'll immediately creating an electric shield around itself if approached too closely, killing Pikmin instantly within its range.
 * Its poison form is the most dangerous form, its body turning purple and bubbles popping from it. It will lay down and roll on the battlefield, making a streak of toxic goo on the ground.

True form
Once it's supposedly defeated, it will go into the water, and come back out as a much larger, gelatinous beast with multiple tentacles, each one a different hazard and element used against you. during this portion of the fight, it stays outside the platform, and whips down the tentacles at you, each one having a different effect on the arena: Use the respectively-colored Pikmin to hit the arms. Each one is relatively weak, and a good swarm will destroy each arm until only the head remains. It'll lean in and shoot out water, and Pikmin can be thrown at it to injure it. Keep attacking until it falls in defeat.
 * Fire arm - slams into the arena, leaving a patch of lava temporarily.
 * Electric arm - hovers above the arena, and launches electricity down at leaders and Pikmin.
 * Water Arm - sweeps over the arena.
 * Poison Arm - whips out poison balls down on the arena.