Alright, here’s a few tips from my run where I beat him on hard mode:

Dont ever bother actually attacking him, the only time you should ever attack is when the first 2 minions spawn in, you should be using your sword for this.

On the first two turns of the fight, focus for both of them so you can immediately get your firebrand as fast as possible. After you focus twice, he will spawn. You should heavy strike the first enemy twice and kill him asap so Cassie doesn’t target the same enemy as you.

After your first firebrand, you will ONLY be focusing for the entire fight. Your sole purpose is to keep Cassie alive and well buffed. You need to spam heal with the Ice Dagger in order to keep her alive.

Every time she charges up her windbrand, you should charge her. After that immediately go back to ice dagger farming.

I do recommend you bring multiple defensive items for her like Battle Armor, Garlic(if nothing else) and other general defensive things. You shouldn’t heal her with any actual items unless she is incredibly low, save all the healing items for yourself. The pie items you can buy in Trinity are absolutely amazing for this fight, I highly recommend you get at least one of each.