Dark Ball

The Dark Ball is an evil technology item and an item featured in the TV animated movie Pokémon 4Ever - Celebi: Voice of the Forest.

History
The origin of the Dark Ball is unknown. The Iron-Masked Marauder is the only person who has been seen using one in the whole series and somehow caught a Sneasel & Scizor. Vicious interrogated a poacher to tell him where he saw a Celebi 40 years ago. When the poacher refused, Vicious used a dark ball to capture a Tyranitar belonging to the poacher and then had it destroy the poacher's entire camp, forcing him to comply.

Eventually he found the Legendary Pokémon Celebi and used the dark ball to catch it. When Celebi turned evil, it turned on it's friends and formed an enormous grass titan. However Ash and Sammy were able to help Celebi break free from the Dark Ball's influence and the ball was destroyed.

Powers and Abilites
The Dark Ball is a unique Poké Ball, way different from all the others. Any pokemon captured by it becomes evil and their power will increase to the highest level. The Pokémon loses its freedom and will obey all commands of its master. It's also able to capture a Pokémon belonging to a Trainer as Vicious a Tyranitar owned by the Pokémon poacher. Dark Balls can change the target Pokémon's color, turning their skin dark.

Weakness
However, the Dark Ball's power can be overcome. If the Pokémon's willpower is strong enough, the Dark Ball that captured it will be destroyed.