The regular enemies with teleportation and stun-lock are generally more dangerous than the bosses in Salt and Sanctuary. I really only had trouble (beyond a couple retries) with two bosses: The Lake Witch and this final boss here, The Nameless God.
Both have a homing/targeted magical/arcane attacks that will eat up shields and health extremely rapidly. The Witch like to spam multiple versions of her attack over and over, I found it cheap. The Nameless God is not as bad, but it still likes to hit you with the magic when backed into a corner, not allowing you to roll underneath the attack as you can for most other enemies.
All that said I was up late watching SNES Super Stars and trying to finish this game before I write up my review for OnlySP. I hit up this battle more than a dozen times, and as you can see it’s not a short walk from the sanctuary to the fight. By this time I’ve learned the patterns enough to know how to win, I just have to avoid the magic attacks, which I do here mostly successfully until the end.
I get trapped twice in quick succession against the wall with his magic attacks, dodging the first, and about to get killed by the second when I pull a downard slash at the last second. A mundane fight until the final strike.