Minotaur has two variants: Minotaur and Gorgon Bull
Minotaur can be a hard fight, even when you have wind magic. His Earth Slide hurts like crazy, as it can cause up to 100 points of damage or more to a character. Fortunately, for you, he does not have the HP to back up his nastiness. He will also cast level 7 Defender, which really does not matter. You will want to have Purim constantly casting level 3 Cure Water to heal the damage of any Earth Slide spells, and Popoi should be focusing some level 3 Thunderbolts onto Minotaur. A few Thunderbolts will take him out fast.
This is basically a rematch with Minotaur, only Gorgon Bull has a level 8 Earth Slide! If you bought the armor from Gold City, it will barely scratch you. His charge attack can paralyze you though, so be careful. Use Popoi's level 4 or level 5 Thunderbolt spell on Gorgon Bull - it does an insane amount of damage.