Here's the build I used to beat them: (post patch 1.03)
Sorcerer Level 145 (Probably don't need to be this high)
Vigor 50
Mind 49 (Needs to be as high as possible to prolong magic attack)
Endurance 27 (Same as above, high as possible to prolong magic)
Strength 10 (Min req to use this staff)
Intelligence 60 (Min req to use this staff)
Weapon: Lusat's Glintstone Staff Upgraded to +10 (Easy to find in a cave in Luirnia Lake)
Used Comet Azur for the first part
Used Meteorite for the second
Mimic Tear +10 Summoned just before the end of the first phase.
Physick Mix: Cerulean Hidden Tear (to reduce FP use) & Intelligence-Knot Crystal Tear (to make intelligence stronger)
Talismans Used: Crimson Amber Medallion +1, Cerulean Seed Talisman, Graven-School Talisman, Old Lord's Talisman (None of these are essential, this is just what I used)
The way to beat the first part easily is hold the run button before you skip the cutscene (and keep it held) and immediately sprint up to the boss and use the Comet Azur spell (remember to hold the attack button to keep the spell going as long as possible). He should just stand still the entire time. This works maybe 90% of the time. If you attack him before running right up to him he WILL generally fight back so wait until you're almost touching him to start the spell.
Second part, run to his side immediately again and use Meteor while practically underneath him and just hope for the best and that he doesn't teleport around the arena too much. Second part took me about 10 tries to get lucky with the RNG and my Mimic hit him a lot too, sometimes he just stood there like a dope and I got rekt fairly quickly.
Good luck!