Think about the timing.
Persuit doesn't last too long, plus you have a good 2 seconds of "casting" before the persuit begins. If you keep your healer/ranged DPS far from Ick & tank, you'll have plenty of distance and warning to start running before he gets near you.
So the fight tends to go:
Nature resist! Totem/food/whatever.
- Healer/Ranged dps at max range (35 yard or so), while rushing in with tank.
- Tank/DPS burn as fast as possible to open, with occasional 5y strafe with healer/ranged dps to stay out of poison.
- Arcane barrage - run tank to healer/ranged dps while hitting /follow.. run in a wide circle around him to avoid explosions. Watch the cast timer, and just when it's about to end, park ranged dps & healer.
- Pull with tank away from group to roughly 35 yards, DPS/burn quick.
- Persuit casting bar will appear.. run with tank to group on /follow.. get as far from Ick as possible without leaving his area. (Don't want him to reset!) You shouldn't have to run away for too long after the time it takes for him to get near you.
- Once he stops persuit, keep running with everyone on follow while throwing instant attacks/casts on him if possible.
- He'll soon cast poison nova, so if you're still running, you'll be far from him when it goes off. If you're worried about it being close, quickly drop nature resist totems!
- Park ranged/healer, use tank to pull him 35 yards from group.
Repeat steps above as needed.
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