On the way to the mountain, Cecil can kill with ease. Once here, however, most enemies are undead and highly resistant to his Dark Sword, so you'll need magic to take many of them out. Palom's Flame magic and Porom's healing spells are effective on the zombies that shrug off Cecil's sword. Or, to conserve MP for when you really need it, use the Flame Rod or more effective but more expensive Holy Arrows for damage, and the Healing Staff for recovery.

The entrance is blocked by flames, but that's no problem for the Nifty Exceptional Wizarding Twins.

Palom's freezing magic puts out the fire, and he starts gloating.

Porom hits him.

Fade out and dramatic music change.

Change scene to a high-tech looking area. Rosa is tied up with a large metal blade suspended over her head (or a large metal ball in the ET and NA versions), while Cain stands guard and Golbeza stands nearby.

Scarmiglione, literally "ruffle-haired", is a demon from Dante's Inferno.

The screen dims as a hooded figure appears before Golbeza.

Scarmiglione disappears.

４てんのう = 四天王. The term has Buddhist roots, but in practice is roughly equivalent to "The Big Four" in English. "Fearsome Foursome" sounds imposing and is alliterative as a bonus. "Four Fiends" is decent, but too explicitly sinister, and while the part about elements is accurate, it's completely extraneous.

Cain drops back and bows.

Scene change back to Cecil's group. A bit farther up the mountain, a familiar old man appears.

Porom hits Palom.

Tella glances at them, then turns to Cecil.

Palom walks over to Porom and says (presumably quietly).

Tella should have a higher max HP than the twins, but other than that, he's rather less impressive now than when he first joined. The twins probably outclass him magically already, and they keep learning more spells and growing as they level, while Tella's spell list and attributes both stagnate. Still, he remains useful as a healer and secondary attack mage, and can use either your choice of rod to supplement damage or a Healing Staff to supplement recovery without using up his limited MP, and it never hurts to have another party member. Give him some better equipment from Mysidia for best results. He can't use arrows, though.

Near the top of the mountain, a strange noise is heard.

There's a save point nearby. Always a good idea to use them, since they're usually there for a reason.

The noise is heard again soon after.

And again at a high bridge.

A cloaked figure appears.

Boss time. Scarmiglione comes with a pack of zombies, but is not actually Undead himself. He has no elemental strengths or weaknesses, but the zombie horde is as usual immune to Dark and weak against Holy and Flame.

This battle is similar to the ones against squads of Baron soldiers in that the minions won't attack until ordered to or deprived of their leader, though here they cast Drain when triggered, with the following line from Scarmiglione:

...rather than simply attacking. The basic tactic is to have Palom hit them all with Fira, hopefully killing all the zombies, with Tella mopping up with Fire if needed. Palom can cast Slow once or twice to give Scarmiglione fewer chances to attack. Tella is mostly on healing duty, though you may very well be able to manage with just a Healing Staff if you realize that Scarmiglione counterattacks all attacks with Thunder. When left alone, he'll alternate between a normal attack and Thunder, and only use either when it's actually his turn. To minimize damage taken, attack as infrequently as possible. The easiest way to do this is to avoid attacking until Palom has used Bravado several times to boost his intelligence, then Pair Cast to wipe him out in one strike. Doing enough damage at once may skip his dying words, triggered when his HP drops below 1000 (it starts at 3500):

Whether the scripted death after his parting lines does it or the damage kills him outright, the battle is won. Don't cross that bridge just yet, though, since another surprise awaits on the far side. Instead, save again, rest if needed, and just before crossing the bridge, reverse the front and back rows. Seriously. Because as soon as Cecil sets foot on the far side....

Scarmiglione appears behind the party, uglier than ever, and another boss battle begins.

It's a back attack, so the front and back rows are reversed, but if you already reversed them, that puts them back to normal. This time, Scarmiglione is both alone and Undead, absorbs Ice, and is weak against Holy, Flame, and Projectile damage. His attack may also poison its target. And he even has a special alternate boss music. Fortunately, he doesn't resist Dark, so Cecil's sword works just fine, and he doesn't even have any special attacks except (maybe) the counter noted below.

It may be tempting to attack with Flame magic, but be warned that he'll retaliate (original JP version only; he doesn't even react in the others):

As sinister as that sounds, it's really just casting Slow on the whole party at once. Still, better to avoid it. Palom and Porom can deal almost absurd (if inconsistent) amounts of damage with Holy Arrows (or any arrows, really, since the Holy and Projectile bonuses don't stack, but Holy Arrows are the strongest so far and easiest to come by), so equip them appropriately, have them and Cecil attack while Tella takes care of healing, and the battle will be over in no time.

Also note that healing spells and items will damage him, but why bother? The twins can easily kill him by themselves with only a handful of arrows.

If you're wondering how these tactics work in practice, here are the results of two sample runs I did, starting with Cecil at level 19, Tella at 22, and the twins at 13. In the first battle, Cecil defended constantly, while Porom always healed with the Healing Rod until otherwise noted. Palom cast Fira, killing all but one zombie. Tella finished it off with the Flame Rod. Palom then used Bravado three or four times, and Porom initiated Pair Cast right after one of these, hitting for over 4000 damage and wiping Scarmiglione out instantly. Palom and Porom reached level 14, and Porom healed the group with Cure between battles to bring everyone up to full health. Porom switched to a Staff and gave the Healing Staff to Tella, while Palom took up a Crossbow and 30 Holy Arrows (since that's all I had on this save file). In the second battle, Cecil constantly defended again (just to see how well arrows really work here), and Tella took over healing with the Healing Staff. Porom started by casting Slow twice, then used the Staff to cure poison as needed or cast Protect on the party to reduce damage taken (when the spell didn't fail). This left Palom attacking every round as the sole source of offense. A mere sixteen arrows later (with several misses), Scarmiglione went down, leaving the party only mininally damaged despite his best efforts to kill them. Another attempt with Cecil attacking and Porom not bothering with Protect had Palom spending just five arrows and left only Cecil at all hurt (a mere 26 damage). Note that in both trials, Tella spent a total of zero MP, and no one cast any healing spells during combat.

He falls partway off the bridge....

...and into the ravine below. There's something strange ahead.

And you might as well unequip Cecil before approaching, even though no one else can use the Dark Knight equipment anyway.

There's a glow, and the party is sucked into a small room with a large mirror for a back wall.

A sword descends, and Cecil takes hold of it. Light surrounds him, and his appearance changes drastically. However, his reflection is unchanged.

Cecil's reflection steps out of the mirror.

The reflection gets in Cecil's face.

Cecil pushes his reflection back into the mirror, and they fight.

As of now, Cecil is a level 1 Paladin with 600/600 HP, 10/10 MP, and the Cure spell, and is equipped with only the Sword of Legend and Clothing, regardless of his previous equipment and level. Becoming a Paladin also changes most of his command list and his entire equipment set. If you bought a Shield of Light in Mysidia, you can equip it now, though it doesn't matter for this battle anyway.

If attacked, the Dark Knight uses Darkness as each of the following messages displays:

The best strategy is to do absolutely nothing. The Dark Knight will use Darkness repeatedly (dealing about 70~110 damage each time, regardless of defense), and after the third time (any used while displaying the above message don't count)....

...the Dark Knight disappears, and Cecil wins.

It is actually possible in theory to win by attacking, but you'd need to inflict 4520 damage without dying in the process. Don't try it.

After more shinyness and a fanfare, Cecil's reflection also turns Paladin.

The twins crowd around Cecil. Tella, on the other hand, looks distracted.

Palom and Porom confer, quickly coming to a decision.

Tella rushes out.

He looks back and forth a few times, then hurries after Tella.

Porom leaves, and Cecil does too after taking one last look back. Incidentally, everyone is now at full HP and MP.

Give Cecil any armoring you have available. The gear from Mysidia is ideal, especially the shield for evasion, but nearly anything is better than what he's wearing. In any case, he can now use basic White Magic in addition to a much larger range of equipment, and his new Holy sword will devestate the local Undead monsters where the Dark swords barely scratched them, all while making a neat new sound unique to holy weapons when hitting. He'll also gain levels rapidly for a while, hardly a surprise given that he started at level 1.

And after being upstaged by a pair of five-year-olds, Tella is impressive once again. His dubious Remember command is gone, but he can now cast nearly any spell in the game. Unfortunately, his attributes remain low overall, and his maximum MP never increases beyond 90, which can go by very quickly with the new high-end spells, but it's still enough to give him an edge as long as he doesn't run out of MP at a bad time.

Out on the field, though, when you're not facing hordes of the living dead, you may find yourself missing some of Cecil's old powers. Without the Deathbringer, there's no more killing the Zuu birds in one hit, and they have a lot of hit points for this point in the game. Darkness worked wonders for mopping up large groups of weak enemies, too, but you'll have to rely on magic for that from now on, or take them out one by one. Still, Paladin Cecil ends up being much stronger in the long run than he would as a Dark Knight.

The party returns to Mysidia, optionally taking a chocobo from the forest south of the mountain.