How I beat this god forsaken dungeon (cheese method):
Have a low level Pokemon with max stats/almost max stats
Set the difficulty to Vanilla, set Level Scaling ON
With this method, enemies will be 4/5th of your level (I was level 61 with 250+ stats, cleared with Uxie) and you will take 1-2 damage from every hit
Bring a Twist Band so your offensive stats cannot be dropped, bring many apples and max elixirs and be patient.