During a special mission, a team of Skylanders discovered a secret lair where Kaos was experimenting with a new discovery – Petrified Darkness – which he initially intended to use to stage a coup against Skylands.
In their fight to stop Kaos, the lair exploded, releasing a cloud of pure Darkness.
The Skylanders knew they couldn't let her escape, so they absorbed this energy, transforming them into dark versions of themselves. Fortunately, Spyro learned to tame this darkness within him a long time ago.
So with his help, these Skylanders have now also learned to control him, combining his power with their own to fight Kaos and the forces of evil.