Wrath of the River King is a 4th Edition D&D adventure project that was designed summer and fall 2008 and released in December. The adventure begins with the heroes approached by a miller's whose bride has been stolen away into the Feywild, and it proceeds through a wild sequence of increasingly dangerous encounters with cruel fey Lords & Ladies to a confrontation with the River King himself.
While the adventure itself is a good follow-on to Keep on the Shadowfell, half the fun was figuring out what works, and watching the process of me flailing about with the 4E ruleset to make it work for the adventure. And it took the opportunity to expand on the Feywild and the role of the fey generally in D&D.
Length grew to about 96 pages... I liked the concept well enough to expand it significantly. Wrath of the River King includes more than a dozen new monsters, plus new takes on standards from the Monster Manual. It includes no butterfly-winged eladrin or pixies, but lots of tough encounters in a darky fey vein, with recurring characters and plenty of opportunities for both roleplaying and combat.
The Wrath of the River King was a limited edition, and largely distributed to its patrons and supporters in November 2008. Copies are available to patrons of Halls of the Mountain King.