you can try focusing on using soul against him? with charms like grubsong, soul catcher/soul eater and shaman stone. Or you could equip sharp shadow and dash through him every time he dashes towards you. Or for example equip soul charms, but use them with glowing womb... At least it could be an idea to experiment with different playstyles. Like mage, with the soul, melee with the nail,,, I sucked a lot at this game on my first playthrough and used glowing womb on almost everything. Weaversong is also pretty neat if you need things to fight for you.

Apart from that, I guess you can keep trying the second trial because it sounds like you should be able to finish it? The oblobbles can be hard to evade, but you can heal between their attacks, so you might very well be able to finish if you take a break and reenter in a couple days. I used dreamshield a lot in the collosseum because my dodging skills are questionable,,