For the last thousand years the Darkling has appeared for three nights every thirty-three years during the eclipse of the three moons and taken one victim each night. When he finally takes his hundredth victim his winds of darkness will destroy all light in the Realm forever.
He abducts his victims by conjuring a purple fog that renders the person with a purple translucency before teleporting them inside the Grotto of Darkness. Hank, Gweekin and possibly Martha's family were all victims of the purple fog along with a flying bug. The Darkling's fog is powerless against Martha's luminescent magic.
Martha destroys the Darkling by engulfing him in her luminescent magic.