So simply I feel like I’ve been banging my head against the wall with this. I’ve beat the Echo Knight in the crucible. He’s hard, but fair there. You have additional modifiers and extra healing from the buff menu you can take advantage of.
As a pestilence boss though, he is so difficult to deal with. First phase in no issue. I can usually get through it without even healing at this point, but the moment the second phase begins the combination of his fast attacks and ranged mix ups make it difficult to fight him. His application of the plague status effect and considerable ranged damage can be really oppressive. Not only are you getting reduced healing effect from the plague effects, but he also will often punish you with ranged attacks whenever you try to heal. It makes the fight overly punishing and difficult. Like I said I will usually not have to heal at all in the first phase. So I will go into the second phase with either 5 or 4 food items left. The moment I try to back up to heal he will punish and kill me from range. Often never actually getting the chance to heal in the fight.
Should be added that the distortion effect that happens in the pestilence can make it harder to discern what attack animation he’s starting up.