Marcellus/Labyrinth of Chaos

Luka's father, testing his son.

Reflects all physical attacks, and does double damage when using yoma/doll/chimara skills.

All of his skills are sealed against a solo Luka.

Biograph
One of the superbosses in the Labyrinth of Chaos. Unlike the rest of the super bosses you encounter on this special floor, Marcellus is not summoned by Luka and co. If you try to summon a boss, Luka and co will feel that something isn't right, and the White Rabbit will call you over. Upon attempting to heal you, Marcellus decapitates White Rabbit and shows up. Naturally, Luka and co are more than surprised. He then points his sword at Luka and demands a fight.

Upon defeating him, he talks to Luka, but this is untranslated. Marcellus than leaves, and Alice/Ilias comment on him.

Attacks

 * Dimension Sword - All Foes, Physical, Physical/Galaxy Attribute, Ignore Deflectors, Dispel, 3 turn cool down
 * Quanta Saber - Random 5 Foes, Auto Hit, Ice/Quantum Attribute, 3 Turn Cooldown
 * Anti Particle Railgun - All Foes, Auto Hit, Quantum Attribute, 3 Turn Cooldown
 * Wave Cannon - All Foes, Auto Hit, Hadron Attribute, 3 Turn Cooldown
 * Ragnarok - All Foes, Auto Hit, Nuclear Damage, 3 Turn Cooldown
 * Shadow Messiah - All Foes, Auto Hit, Dark Attribute, Death 10%, 3 Turn Cooldown, 10 MP
 * Monster Lord's Slash - All Foes, Physical, Yoma Slayer, 3 Turn Cooldown
 * Artificial Dematerializer - All Foes, Auto Hit, Yoma/Chimera Slayer, Imbue Chimera Slayer for 5 Turns, 3 Turn Cooldown

Strategy
A step up from other fights, Marcellus isn't fooling around. His most dangerous attack is the one that killed White Rabbit, Dimension Sword. Barriers such as Electromagnetic armor and Victorious Clara are ignored, but that's not all, it also dispels all buffs on your team! Beyond the first time you encounter it (Because of endure), it is highly likely you will lose a party member every time he uses it... if weren't for the fact that it ISNT an auto hit attack. Thankfully, the Lamia's dance: Waning Moon Dance, prevents the damage from it, however, due to the dispel effect, it will only help for that one attack. The rest of his moves aren't a pushover either, as they are the special Chaos element type. For example, if you were completely immune to ice, Quanta Saber, with its Ice/Quantum attribute, would ignore it. In other words, there is a Chaos element for every normal element, and these Chaos elements bypass any elemental nulls/absorbs. For this fight, Nuclear is Fire, Quantum is Ice, Hadron is Wind, and Galaxy is Physical (Carnage is also Physical, but its unsure what the difference is between them) His second most dangerous attack is the previously mentioned Quanta Saber, which hits 5 times and is likely to 1 hit KO anything it touches.

Oh, and Marcellus, like the Apoptosis that he fights, also completely reflects all physical type damage, and actually Nulls both Physical and Pleasure damage. Since most weapons (Barring Sex Toys and Harps) add physical damage when using them for a skill, this means without LoC gear, you are stuck with magical attacks and the occasional auto hit attacks. However, he also negates Dark attribute attacks, so don't use those types of auto hit attacks. Like many other super bosses, Marcellus basically is immune to status effects, barring slow. But at a 25% chance to inflict it, its pretty much worthless, as most of Marcellus's attacks are auto hit and his evasion rate is 0% anyway, and without LoC gear, Marcellus should always go first.

Apart from that, there is no short cut to winning, only properly keeping track of when Dimensional Sword is up and hoping to get one good combo on Marcellus.

Check here and here for detailed information on all the superbosses and everything you can make use of to defeat them.