You fight the Four Archfiends from FF4, with one in a dungeon (similar to Genbu in SB. Earth Archfiend is kinda a pushover in FF4 cuz he is an undead, thus weak to both fire and holy), two in trials, a solo instance where you fight the Fire Archfield, before moving to the final trial where fight all four archfiends at once. Then they merge in Phase 2.