As Yex and helmsman don't have any weak points, you can't crit them (except with a sword parry ), which makes critical focused builds very weak against them. They're the only bosses like this, It creates a huge imbalance between waves, when it takes a few dozen bullets to kill one boss and the next requires hundreds. And if the game apply a hunter eminent card, it makes bosses impossible to fight if you don't change the card before the fight.
