Deathknell creates a custom healthbar as an enemy approaches ToD range, giving you plenty of warning so that you can make the most of your Five-point Palm Exploding Heart Technique! The in-game Death Note buff and spell-flash are not very responsive, which tends to cause bosses to die long before you are notified by the default UI, or any aura addons set-up to watch for the Death Note buff; this gets around that problem.
Type /deathknell <arg> where <arg> is worldboss, rareelite, elite, rare, normal, trivial or minus to toggle Touch of Death healthbars for different classes of enemies. Type /deathknellnotify <arg> where <arg> is worldboss, rareelite, elite, rare, normal, trivial or minus to toggle Touch of Death notifications in the same manner. Notifications are Raid Warning style call-outs in the middle of your screen, with an accompanying sound effect.
The bar can be moved by holding Alt and dragging.