After Sacred runs from you in the pervious boss fight you must accomplish several things before going to the center of your map to battle these two bosses, Sacred (who ran from you earlier in the game) and Minotaur (Sacred's brother).
HP: 855- 36,375
AP: 20
Weak vs. Poison and Wind
Immune to Earth
Minotaur
HP: 578- 27,218
AP: 20
Weak vs. Wind and Poison
Absorbs Earth
From there use your map to guide you to the Western most room and you will find the second switch in the left hand corner or that room. Press the X button and flip the switch.
You now have access to the center of the map, where the two bosses are.
This fight is basically the same as the Sacred battle. You basically use the same strategy but now you have two bosses and Minotaur is allot more powerful than Sacred so you have to be more careful.
A healthy supply of Float spells is a must during this game otherwise the two will keep on absorbing HP from the Earth and this battle will be very long and very hard. Also cast float on all of you party members
because Minotaur's Mad Cow Special (which is very powerful) is an Earth-based-Attack so is Minotaur tries to attack it will not effect you char, instead it will pass harmlessly below.
Even though casting Float on everybody leaves your enemy's virtually harmless you will be happy to know that basic attacks work well in this fight and also if, you choose so, boosted GF attacks work well too. All
in all this shouldn't be a tough battle to win.
After defeating the two you will achieve the Sacred card, the Minotaur card, and the two join you as a GF.