Pokémon, originally intended for children, surprisingly harbors many dark moments and sacrifices.
1. Confrontation with Sabrina

Sabrina stands out as a character that sends shivers down viewers' spines due to her eccentricity. Possessing unique psychic abilities, she exclusively favors Ghost and Psychic-type Pokémon. What makes her particularly unsettling is her penchant for teasing and even tormenting others for her own amusement.
In the episodes 'Abra and the Psychic Showdown' and 'Haunter versus Kadabra,' Ash undergoes a harrowing experience confronting Sabrina. She forces her Pokémon to evolve and goes as far as using others, including her own mother, as mental prisoners for her entertainment. This sadistic approach leaves lasting emotional and physical scars on those involved.
2. Spearow's Attack

Pikachu and Ash's first encounter was electrifying from the start. In this initial meeting, Pikachu shocked Ash into a state of uncertainty. Due to Pikachu's disobedience, Ash struggled to catch any Pokémon thereafter. Frustration took over, leading Ash to throw a stone at a Spearow's face.
Ash's recklessness angered a swarm of Spearow, resulting in a fierce attack on both Ash and Pikachu. The duo had to flee, evading a relentless wild Pokémon chase. Escaping into the water with a young child proved to be no easy feat. Even Pikachu was shocked by how injured its trainer was after the first battle.
3. Gary's Showdown with Mewtwo

Ash never directly faced Giovanni, the boss of Team Rocket, in a one-on-one battle. However, Gary Oak, Ash's primary rival, had the chance to clash with Giovanni. Through this battle, Gary learned the difficulty and terror of confronting an antagonistic boss.
Indeed, it was a truly eerie battle for Gary. The arena was dark, empty, and Gary couldn't locate his opponent. Initially performing well, Giovanni then unleashed his trump card - a Pokémon absent from the Pokédex: Mewtwo, equipped with battle armor. Mewtwo easily defeated Gary, leaving his Pokémon severely injured. When Ash found Gary, he was in a trance, repeatedly muttering the words: 'Pokémon devil.'
4. The Tree of Beginning and Lucario's Sacrifice

In the Pokémon movie: Lucario and the Mystery of Mew, Ash and his companions encounter a Lucario defending its kingdom. After gaining Lucario's trust, the group helps it journey to the Tree of Beginning to rescue Pikachu. What seemed like a straightforward adventure turned into significant trouble for the team.
The Tree of Beginning is not only guarded by the legendary Pokémon group, the Regis, but also possesses a formidable defense system. Its resistance system can swiftly engulf both humans and Pokémon. It wasn't until Mew appeared and used its powers that the terrifying influence of the Tree of Beginning could be neutralized. However, Lucario had to sacrifice itself to bring everything back to safety.