Once upon a time there was a potato. No one wanted the potato because at its core, instead of anything edible it was only piano black inside. Also the potato made too many suicide jokes and self deprecating comments. It also had split personality disorder. One voice was to blame for all the suicide jokes and self deprecating comments. The other was alternately chastising the suicidal voice and waxing poetic and nihilistic.
One day, the potato ran out of chocolate milk, and became severely depressed as a result. As it sat forlornly it began to think. Or maybe one of the voices thought, "The world is a mess. And humans are the cause. What is their purpose? They don't have one. I should fix the world. Eradicate the humans, let the wild things come back. Yeah that'll probably be better for everyone."
And so the potato began to scheme. It had no arms or legs with which to enact any plan, so that was the first thing that needed to be corrected. And so the headline flew around the world. "Breaking News! Potatoes Capable of Thought!" And humans, in their mindless naivety and arrogant belief in their own superiority built the potato, and other potatoes, child size bodies. This was of course, according to the potato's plan.
It snuck out of the lab in which it was contained and began it's quest. Well, snuck might be the wrong term. It took a scalpel and slit the throat of every scientist it came across. It was very thorough and no one was the wiser, mostly because humans are very two was accomplished with a shocking amount of ease. Of course, no one knew the potato had gone rogue, as any who had known about it were now dead, so perhaps that aided in the potato's mission. No one knew how the potato got ahold of the nuclear codes, but Washington D.C. was the first to go, followed quickly by New York, Geneva, Tokyo, London, Nevada, and Massachusetts.
Soon after, Antarctica was blown up, but this was not the work of the potato. There was another sentient plant, a maniacal tomato with a god complex. The tomato shared the same ideals as the potato, however the tomato, rather than being depressed like the potato, was in a constant state of extreme excitement . The potato learned of the tomato's success against the Penguin Army of the Antarctic Nations and offered a temporary alliance to speed of their plan of the removal of the human species.
The annihilation of Antarctica resulted in the mass global flooding, drowning many coastal nations and pushing civilization inland towards the mountains. However, this followed the Tomato's plan exactly, to herd the human race like cattle, so they could exterminate the population with fewer nukes. The potato followed that up with several missiles to the new coastal cities, crowding the population into the mountains.
With the humans condensed into smaller areas, the potato no longer had any use for the tomato and was getting quite annoyed at the tomoto's perpetual joy, so it left the tomato in the Rocky Mountains and blamed all of the death and destruction on the tomato. Humanity did what it does best, overreact and kill everything without thinking first, and stomped the tomato into ketchup.
With the tomato out of the way, the potato was finally able to launch the last nuke, aimed for the bottom of the Marianas Trench. The resulting explosion would trigger the Ring of Fire, the Yellowstone Super Volcano, and also the apocalypse.
"Why!" a dying human begged. "You'll die too!"
For the first time the potato spoke. "All according to plan."