The History of Death Coil (Vanilla WoW to Mists)
680At launch, warlocks death coil would deal damage and heal the target for 100% of the damage it did on a 10 minute cooldown which was later changed to a 2 minutes and healed for 300% of the damage. It also applied a horror effect which was a 1 of a kind effect that only warlocks had until Priests were given pyschic horror. A horror is not a fear, so things that prevent fear like berserker rage and fear ward did not work on it. also it does not break on damage. Its basically a stun that is on a seperate DR. So death coil was pretty great. Also until patch 2.1 it didn't have a diminishing returns so warlocks could chain deathcoil after deathcoil as much as they wanted in arenas.
Then in mist it was renamed to Mortal coil and and made into a talent. This new Mortal coil had a shorter 45 second cooldown and healed the lock for 15% of their total health.
The deathknight Deathcoil was used to deal damage to enemies and heal undead allies. When a deathknight uses lichborn they become undead and can use death coil on themselfs to heal. This, combined with old school glyph of deaths embrace which refunded 20 Runic power if used to heal, and glyph of deathcoil, which increased its damage and healing, gave DK's a really nice self heal. Although at the time these two glyphs still worked like that, Deathknights also had a couple other really good self heals. Deathknights were just overall OP in Wrath.
Eventually both these glyphs were changed to only refund runic power when used on ally minions, and the ability to be used on any friendly target to give them a shield that absorbs damage.
Deathcoil is also the main runic power dump for Unholy and as such has gone through a lot of changes for that spec. None of which are really all that intresting so I'm not gonna list them. But Currently when you use deathcoil 5 times as unholy you can use dark transformation to turn your minion into your own pocket warrior.
Warcraft 2 and 3 footage used from Krisw39
http://youtu.be/Z191ACJ0gVM
http://youtu.be/o0Jv7y0LVAA
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