According to old tales, these Pokémon are stumps possessed by the spirits of children who died while lost in the forest. (Y)
It's important to remember that with non-Legendary Pokemon, there are many of them. Hordes of them, all over the place. The same goes for Phantump, a Pokemon composed of the dead souls of children who perished in the woods. The concept would mean that every one of the seemingly infinite number of Phantumps out there are collections of dead kid spirits, meaning a) wow, LOTTA dead kids lost in the woods, I guess? and b) every time you defeat a Phantump, you are actually laying waste to a group of eternally-lost kid spirits. Makes you wonder: who's the REAL pocket monster?
It enwraps its prey in its hair like arms. It sings joyfully as it observes the suffering of its prey. (Y)
Nothing is safe in this world (in case that wasn't already super, super clear). Enjoying a pumpkin spiced latte? Well, the pumpkin that died so you could enjoy that turned into an evil pumpkin ghost that wraps its appendages around living beings and SINGS JOYFUL SONGS as whatever poor creature dies a miserable death. I would never wish "strangled to death by a ghost-plant who was humming Katy Perry songs" on anyone.
When its life comes to an end, it absorbs the life energy of every living thing and turns into a cocoon once more. (Y)
Good to know that literally ALL LIFE completely depends on the survival of one big red bird thing, that - while pretty strong - could easily get decimated by an ambitious 11 year old trainer who's grinded his Chestnaught and Charizard to level 100. When this thing dies, we all die. All life on this planet - humans, animals, Pokemon, etc. - comes to an end in an instant. This is why it's better to go after the rainbow reindeer. At least Xerneas won't destroy all existence if you accidentally faint it.
Darumaka's droppings are hot, so people used to put them in their clothes to keep themselves warm. (White)
Even for a world where all of society seems to only care about magical monsters that are constantly beating each other up, the idea that people are putting hot monkey poop in their clothes to keep warm is somehow the most unbelievably disturbing thing I've heard of in a Pokemon game.