After beating the game once on easy difficulty I have beaten every mode on normal and after that every mode on hard (ever since then I'm hard difficulty only). The only thing that I haven't done yet is hard-pacifist-descent and only 'cause I got bored too fast and then accidently started a new run, but I didn't had the right mood to repeat until -80 something lvl on pacifist again, so I just forgot about it for some time.