The Captive Digimon Digimon: Digital Monsters : Season 2 Episode 10

Ken creates the Dark Spiral, a new version of his Dark Rings, to be able to control ultimate-level Digimon. Conflicted, Wormmon, Ken's Digimon partner, frees Agumon hoping Ken would use him for his experiments. However, as Agumon reunites with Tai, Ken recaptures him with his new Dark Spiral and makes him Dark Digivolve into a MetalGreymon's virus form and attack the DigiDestined.