Killed by the Knights of Hell

“	Castiel: This is a massacre. Cain: Yes. And soon it will be a genocide. My children, my whole poisoned issue. Lot of them out there right now -- killers, fighters, thieves. Some more peaceful than others, but they still carry it -- the disease. If the Mark wants blood, I'll give it mine.	”
	— Castiel and Cain in The Executioner's Song

Beings killed by the Knights of Hell.

Demons[]

All of the Knights of Hell except Abaddon, Cain and Dean - Slaughtered by Cain with the First Blade in response to the Kidnapping of Colette Mullen.

Abaddon's Demon Army - Smote by Cain during an attack at his house.
Abaddon's Demon Guards - Smote by Cain while rescuing his wife.
Cecily - Stabbed by Abaddon with an angel blade in response to Cecily giving Crowley information.

Henry Winchester - Fatally impaled in the abdomen by Abaddon.
Larry Ganem - Throat slit by Abaddon while possessing his wife in 2013.
David Ackers - Neck broken by Abaddon.
Ted Bowen, Mr. Markham and a large amount of the Men of Letters Elders - Brutally slaughtered by Abaddon on the night of August 12, 1958.
Entire American chapter - Slaughtered by Abaddon on August 12, 1958.

Abel - The first murder. Stabbed by Cain with the First Blade as part of his deal with Lucifer to ensure Abel's soul ended up in Heaven.
Colette Mullen - Several bones snapped by Abaddon while possessing Colette, accidentally fatally wounded by Cain with the First Blade.
Comic Store Clerk - Killed by Abaddon for her clothes.
Dozens of Cain's descendants - Slaughtered by Cain out of a belief that his bloodline is tainted by the Mark of Cain.
- Leon Tolliver - A convicted felon from Orlando killed by Cain as part of his slaughter.
- Tommy Tolliver - Serial killer stabbed through the chest by Cain with a knife as part of his slaughter.
Gavin's friend - Telekinetically impaled upon a metal hook in 1723 by Abaddon.
Hotel Manager - Throat slit by Abaddon with her nails.
Larry Ganem's wife - Killed by Abaddon alongside her husband.
Max Thompson - Ripped apart by Abaddon on August 5, 1958 after Hell learned that he had cured a demon.
Unnamed man - Throat slit by Abaddon for a Goblet of Blood call with Crowley.
Thousands of unnamed people - Slaughtered by the Knights of Hell over the centuries they were active, particularly by Cain.

Donkey - Killed by Cain to forge The First Blade that can be powered by The Mark of Cain.