Doom

Doom is the name given to a powerful, sentient, and diabolical entity and its corruptive essence.

=In fanon games=

In Pikmin: Ultimate Doom
Doom is the final boss of Pikmin: Ultimate Doom. He is a ruthless being of utter destruction, as indicated in the Ballad of Thames Zweihander.

The Void rips through the fabric of reality and two glowing eyes can be seen. A sinister laugh followed by an utterly cold voice sounds.

“So, you thought going to a distant galaxy ten thousand years in the past could separate us? Wrong. Going to the Andromeda Galaxy has helped my cause very much. Without the Spire of Being and Tower of Balance on Earth blocking my grasp, I can manifest before you. You might wonder who I am, and what I am here for. Some call me the devil, others say I'm a myth. But what matters is that here I am, in the core of this plagued dying moon, existing just before you, Olimar. It was I who instigated the ultimate destruction of Earth, a once flourishing haven for power, now a sad shell of itself. And I will continue to put much of my existence towards the breaking down of the planet. We seem to have a conflict of interest. And I intend to extort my will over yours. So, do you and your leafy comrades have the heart to stop an ultimate being? Regardless, here I come. Here, now, ultimate and absolute, Doom.”

When you finally defeat Doom, his final form kneels before Olimar.

“So I can see that the sheer goodness of your heart can slay the utter devastation of my soul. They say mortals are stronger, and now I understand. Immortals stretch out their life so much that they have little power forever, and mortals have such short lives that their power is immense and fresh. How I wish, in my dying breath of existence, that I'd paid more attention to the little things in life. Maybe, just maybe, my terrible life would've been slightly better...”

So ends Act II of the story.