If a merc loses too much confidence they will panic and suffer from a stat decrease. Avoid this by keeping aggro. huh?
I am not sure how this works for tank mercs but if the merc gains agro from I believe 3+ mobs they stand there and do /cringe emotes over and over. Their stats take a dive as well. Edited to say yeah I hate it too, give them master spells, more of their class defining spells, CURE CURSE, and the ability to dodge on red text. I know we already had this talk on beta but... If a casual player is afraid that a merc will take their place in a group then who is to blame there for slack?