Plague monks and Berserkers can be incredibly frustrating to fight, often because one or two might be locked on to your friend so you walk over to help and instantly lose half your health because it was on you the entire time, just walking and swinging in the other direction.
I feel a berserker on you should have a visible indicator that they’re going to wreck you if you get close that is not there when they are not targeting you. Normally you would just try to infer from the animations but often times they will happily walk backwards while attacking forwards, move in complete opposite directions, or do other incredibly unreliable and conflicting behaviour that muddies your overall assessment of what they are doing. Coupled with the fact that they hit so incredibly hard, it means an incorrect read of that particular enemy is devastating and very unfun.
As such I think when a zerker is attacking you it should add some sort of indicator, say a dark aura to the edge of your screen, or something more subtle like trailing glowing eyes of that specific unit. This effect would then go away once he is no longer locked on to you.