Dark Evolution (暗黒進化 Ankoku Shinka, ダーク進化 Dāku Shinka) is a corrupt form of normal evolution. It is usually triggered by the negative emotions of a Tamer being so great that they have a negative effect on their partner Digimon, initiating evolution to a "darker", generally uncontrollable Digimon. In Digimon Adventure 02: Digimon Hurricane Touchdown!! Supreme Evolution!! The Golden Digimentals Lopmon Dark Evolved to Wendimon through rage and hatred stemming from its loneliness (though the English dub states it was due to a virus). In Digimon Adventure tri. Meicoomon Dark Evolves to Meicrackmon: Vicious Mode because of the infection whilst Nyaromon Dark Evolves and Warp Evolves at the same time to Ofanimon Falldown Mode, though Toei Animations website for tri. indicated it actually evolved through each of its stages one by one and then Dark Evolved as Angewomon. In Digimon ReArise the Spiral are able to force Digimon to undergo Dark Evolution after possessing them. In Digimon Adventure:, the miasma corrupts both Taichi and MetalGreymon and force MetalGreymon to dark evolve into Mugendramon.
When Taichi aggressively forced Agumon to try to super evolve in "Dark Evolution! Skull Greymon" with disregard to Agumon and the others' feelings Agumon evolved into Skull Greymon. In this form Agumon lost all sense of himself and attacked anything and anyone nearby.
Digimon Adventure tri.
In Coexistence, Hikari becomes deeply depressed due to her brother's disappearance. As a form to fully release Meicoomon's destructive power, the Mysterious Man converts Hikari's bad feelings into viral data, forcing Nyaromon to dark evolve into Ofanimon: Falldown Mode, that later fuses with Raguelmon into Ordinemon.
A dark evolution occurs when Yagami Taichi gets swallowed by Done Devimon while Metal Greymon: Alterous Mode watches. He was completely succumbed by the miasma which his hate and anger felt by the latter pushes him and the miasma force him to dark evolve into Mugendramon.