I couldn't finish 'em. Looks like this's gonna get complicated.
Great Galdes is a superboss in Final Fantasy Crystal Chronicles: Echoes of Time. This fight is the exact same as the final boss fight from Ring of Fates, only the difficulty is ramped up significantly by the small stage and rapid rate of crystal respawns. It is highly recommended to destroy the crystals as soon as possible to avoid having too many spells targeting the player, and then focus all fire on Great Galdes, though the player should be wary of his target ring.
Great Galdes has access to the extremely powerful Meteorga, which can inflict heavy damage, if not outright kill anyone caught in it, as well as Stun, Graviga, which can leave players helpless with the Gravity status should they find themselves in the stair pit, and Quaga, which knocks players into the air as well as deal heavy damage.
Great Galdes will summon the crystals continuously, as well as revive the spikes around the base of his pillar. Destroying all of the spikes will make Great Galdes reveal his weak point, which is inside the mouth on front of him. However, attacking this weak point can be troublesome, as standing on the pillar will prompt Great Galdes to constantly cast Meteorga on that player.
It is highly advised to attack it a couple times, then leave quickly and circle around Great Galdes, then continue attacking him from there. Unlike in Ring of Fates, Great Galdes does not have a second phase to the fight, and once all of his HP is gone, the fight will end.
Of note, Great Galdes is the only enemy in the game to use Graviga, Meteorga, and Quaga.