Earlier today, we reported that the Fel-Infused Freight damage on the Zaen Bladesorrow encounter was "fake damage". It would show someone's health bar going down, but in reality, your health was actually full the entire time. This bug appeared to have been in since the start of the expansion, but it has now been hotfixed.
This boss is now substantially harder for your healer and deals a very high amount of rot damage. In addition, missing a green barrel will almost certainly wipe you on high keys, so make sure to destroy them every chance you get.
