The Killer's Blade is a iron sword with alot of enchantments.
Apparently Herobrine had it at one point and killed a few noobs...
"You notice Red Stains."
"You hope it is ketchup."
In the command you can replace the "@p" with your username if you don't want everyone getting a Killer's Blade. Also, the command is already minimized, so you don't have to worry about anything.