You right, that was my 8 or 9 attempt, I decide that only way to do it is to have no purple monster in 1st wave and no more than one in second (so no items went easy)
I was lucky enough to didn’t get any purple monster (what makes my run totally not spectatular) but there is nothing in rules saying that you need to kill at least 1 purple enemy or something so I decide to post it
Also in first try with mono purple I bring purple enemys health to 300 something but I gave because it took too long and I used most of my healing