Rhapthorne
Rhapthorne appears in the final chapter of "Black Citadel." Because Rhapthorne is the game's final boss, he is also one of the most difficult to defeat. Rhapthorne appears in two forms. The first is as a large, purple blob with wings. His second form is his primary physical form, a larger, more powerful version of his first form. Rhapthorne gets two attacks per turn. While these attacks don't cause much damage (100 or so), his "Desperate" attacks can cause up to 300 in damage. Most of Rhapthorne's attacks are magic based. Attacks such as "Kaboom" results in 70 to 120 in damage to an entire party in one turn.
Ruin
Ruin also appears in "Black Citadel." He is capable of smashing entire castles. Ruin's only mode of attack is "Smash!," which inflicts up to 300 in damage to a character. Once you figure out the right sequence of attacks, it's just a matter of repetition before you take him down. Defeating Ruin awards 2,480 experience points.
Marcello
Marcello was once an ally, however, he's come under Rhapthorne's possession. Marcello's attacks generally focus on one party member at a time. His primary physical attack causes about 100 in damage, though his "Kafrizzle" spell can cause up to 120. Marcello's multiparty attack can deal between 100 to 120 in damage to an entire party.
Gemon
The dark, winged creature Gemon is one of the easiest monsters to defeat. Gemon arrives with his henchmen Dark Condor and Dark Turkey. They are weaker than Gemon, making them more of a nuisance than a problem. Gemon has a powerful physical attack called a "Desperate" attack, which can do up to 300 in damage. Gemon's "Blast of Fire" is a multiparty attack that can do 50 to 75 damage to the entire party.