Difficult. I have nothing against difficult games by the way. The only issue I have here is all bosses dealing damage on contact, even when they are stunned.
I play on keyboard and I dashed through a boss sometimes when I'm left with little space. The invincibility window isn't long enough to pass through the whole boss. Or I accidentally bump into them when I use dash to reach the stunned boss faster. Maybe it's just a skill issue though.