I'm so sorry I completely forgot about this.
Try using a melee build. Black katana from the smuggler at the docks at night. Shirt of rage and cloak of speed.
I don't remember the exact build I had forgotten this but these were the core items which boosted my attack and evasion.
I also had the Uberlab mode from training with the hermit, Ring of luck and bunch of greater healing potions from the infinite money trick.
Edit: these were my stats at the end of the game from my current safe file.
You can cheat on Joiplay if you need.
For a mage I would equip Cloak of Speed, Adamantite Helmet, Warlock's Ring and Amulet of Mana. You can also trade 10 max HP for 20 max MP indefinitely at the Academy of Magic, so between HP and MP, HP it's always better. At the statue in the beginning you can gain 50 max HP (equals 100 max MP later), after finishing the quest at the cemetery you can also choose between a potion that expands you MP by 50 or your HP by 100 (this can become 200 max MP at the academy). With 750 max MP and Amulet of Mana, you regen 75 MP every turn, making the battles a lot more manageable.
