Poké Wars/Nightmare Fuel

Even when it is cute cartoon creatures doing the fighting, war ain't pretty

The Pokemon attacks provide most of of the Nightmare Fuel. But the Pokédex entries from the games add even more Nightmare fuel.
These two lines:

Skitty screamed both from the pain of the impact and the indescribable agony that arose from the corrupted blood that coursed through her veins, destroying everything they touched. She fought through the pain, struggling to get up before anything could take advantage of her vulnerable state. She tried to get up only to have her legs buckle. Her strength left her as the Ariados venom in her blood began to slowly digest her organs.

She [Solidad] opened her eyes; the scene of her Lapras dying still replayed over and over again in her mind. No matter what she did, she could not erase the sight of Lapras's eyes bursting and her skin scorching as thousands of volts surged through her body, burning her alive.

Pinsir moved in the way, taking the blow for its master, its friend. Samurai watched, horrified as the process was already starting. Tiny Weedle shaped figures crawled beneath Pinsir's flesh; cracks either coming from the movements within its innards, or their feasting were heard.

Given what the Pokedex entries from the games already can give, this has plenty of it; both shown like a poor Nurse Joy being found with her eyes fused shut and likely boiled away by electrical burns after a electric Pokémon attack in the first part of the series and implied. Who knows what horrors Pallet Town suffered at the hands of the flying drills/spears that are Spearow/Fearow. Ash's mom Delia is revealed to had already died during the first wave of attacks and Oak is shown dying when Ash meets again and soon passes away after giving him a last wish to find Gary.

The world in general is going to hell because of Ho-Oh removing the dampeners and reverting them to their baser instincts, making it a nightmare considering everything that's happening:

Mesprit: It seems like every poison Pokémon has their own agenda. They don't care who they hurt. The Muk are destroying everything in their path, nature, Pokémon, humans, and their creations included. Their very presence poisons the earth. Once they touch a piece of land, nothing will ever grow there for years! Every breath makes the air toxic, and if they reach the sea…" (trails off, shuddering at the unimaginable disaster that would unfold, then regains her composure) I can't see how this fits into Ho-oh's plan of helping the environment!

Mesprit: The Beedrill and Combee have become mindless drones; they're killing anything that comes near their ever expanding hives. Zubats have become bloodthirsty and as long as something has blood, they don't care who they kill and that's not even the worse of it all. (now on the verge of crying)

Mesprit: Raikou has been stationed near the center of the Johto region; he seems to be guarding a human tower of metal. Entei's been destroying entire cities to the southeast of the region. He's trying to find a method that works fastest for killing every human and leveling any standing human structure in the area. (teeth gritted together in rage as tears flow down her cheeks)

- And worst of all, Mesprit is the embodiment of emotions for humans and Pokémon alike, meaning she felt everything ounce of blood-lust and terror, which basically hits her the hardest.

Mesprit: …and I had to watch it happen! (finally cracks and breaks down into tears)

In Poké Wars: The Truculence, there is a very graphic scene of an Officer Jenny being dissolved alive by a Muk.