And this is one of the other stories that I was originally planning to write for Terrifying Tolkien Week. I finished the writing during NaNo, but I am just now getting around to editing. I started this from a quote in the Appendices that caught my interest about the history of Gondor.
Summary: In 1944 S.A. Gondor was attacked a second time by the Wainriders from the far East.
"In 1944 King Ondoher and both his sons, Artamir and Faramir, fell in battle north of the Morannon, and the Enemy poured into Ithilen. But Earnil, captain of the Southern Army, won a great victory in South Ithilien and destroyed the army of Harad that had crossed the River Poros. Hastening North, he gathered to him all that he could of the retreating Northern Army and came up against the main camp of the Wainriders, while they were feasting and reveling, believing that Gondor was overthrown and but nothing remained but to take the spoil. Earnil stormed the camp and set fire to the wains, and drove the Enemy in a great rout out of Ithilien. A great part of those who fled before him perished in the Dead Marshes" (The Return of the King, Appendix A, pg. 370-371).
The Wainriders who fled from the rout experienced the terror of the Dead Marshes, and few escaped alive.