It says you can haunt 1 player to either do more dps to him or take less dps (depending on stance). If its really only one player and then the gem goes at cooldown you will have a hard time to control that at a normal bg situation, the curse could hit the wrong person instead of the big and strong guy which causes you trouble.
If the gem can haunt groups of players then it would be sure good but from what i understand so far it is more a 1vs1 gem and such situations are rare.
Edit:
Nevermind, was reading it wrong and it seems that you can curse multiple enemies at the same time but the same person only each 20 sec. Its sure powerful then and maybe even a great replacement for frozen heart.
Haunt Coil (Five-Star Gem): When you deal damage, you have a chance to haunt the enemy for 6 seconds. Haunting an enemy while in Offensive Stance will cause them to take increased damage from you and haunting them while in Defensive Stance causes them to deal reduced damage to you. Additionally, haunted enemies will unleash blasts every 2 seconds, dealing damage to surrounding enemies. Enemies hit by multiple blasts within 2 seconds take reduced damage from subsequent hits. Cannot haunt the same enemy more often than once every 20 seconds.
It looks like a 5* variant of the Beherit gem. However, 30 sec cd on stance may be a heavy bottleneck for it, despite the 20s cd on both effects. 10% proc chance is better than bile but 10s with no effect is kind of huge.
Hopefully, NED and potency could close the gap but mainly for high profiles.
I am not a hughe fan of this stance swap and that will maybe be the reason why i skip this gem. But without a new socket it is unlikely that i level new gems anyway, i cant replace the now very solid gems which are left at my setup.
Ok, i read again my post and there is no 10s without effect
Every 20ish sec it will proc, then depending on the stance the effect will be different.
I’ve started lately to use more the stances, espacially to have the defensive one ready during fights. Offensive one is a nice buff with new Pikachu build for burst.
Ye, it has a chance to proc every 20 sec at the same person (effect depending at current stance) but even with that i feel it is more and more useless to keep beeing up to date with gems. Bg feels total random if you win or loose and as a sader the imbalance is so strong atm compared to other classes that i ask myself why even bother anymore for new gems or gear (the new fist of heavens build was only working at tower for me and at the shadow war map not at the bg´s).
I think i will skip it this time and save some money, having already so many good 5 stars dormant is another point which holds me back.
So maybe I’m misinterpreting what it says, so let me know if I’m wrong.
The way I understand the description is the same enemy has to wait 20 seconds before that enemy can be haunted again. (a 2nd time)
So really, it’s always haunting, always adding extra damage to every enemy in range. The 20 seconds cool down is for a 2nd hit on an enemy that has already been hit once. Depending on the percentage this could be an extremely powerful gem.
Engage → 10% offensive proc (6sec ish)
Low life ?
Change stance → 10% defensive proc (6 sec ish)
30 sec cd for stance but a other proc possible for a tank that can last 20 sec in between, which is possible with shields and CoL for cruz and also for druid/bk/barb.
Depends on how long last the fight (if OS then useless )
)