Yacht Club Games reveals details on Shovel Knight: Plague of Shadows, a new expansion for Shovel Knight that's coming for free to all owners of the throwback platformer next this spring (thanks nin). They offer some screenshots along with the following description:

Shovel Knight: Plague of Shadows is a free expansion for Shovel Knight, a sweeping classic action adventure game that won over 70 Game of the Year Awards in 2014. You play as Plague Knight, the villainous master of alchemy, in a quest all his own. Using his maniacal scientific mind, Plague Knight is seeking to concoct Serum Supernus, the Ultimate Potion. However, to retrieve these ingredients, he must extract them from his former allies… the villainous knights of the Order of No Quarter! World class platforming, music, storytelling, and art all return in Shovel Knight: Plague of Shadows; an explosive quest with a new play style, new story, new bosses, and more!