The monsters of darkness that have taken over the crystals. They must be defeated before the crystals can be reawakened.
- Doomy Dooms of Doom: All four of them have "doom" as part of their Red Baron titles.
- Expy: On the whole, the creatures of doom who invade the four crystals are clearly a second take on the 'Four Fiends' of Final Fantasy I, with Gigas Lich in particular almost certainly serving as a Shout-Out to the first fiend of that game, Lich, the Fiend of Earth.
- Puzzle Boss: Like the Jobmasters, they have patterns and moves that make them very challenging bosses if you intend to brute force them without any strategy, as they are all powerful and soak up lots of damage if you do. Learning their gimmicks and patterns, and what you can do with them, makes them much easier to handle.
Orthros, the Bringer of Doom
The dual-headed beast that guards the Air Crystal.
- Achilles' Heel: Predictably, the ice head is weak to Fire attacks, and the fire head is weak to Water attacks.
- Breath Weapon: Has both an ice and a fire one. While the two heads are alive he can combine them into the devastating attack Blazzard.
- Does This Remind You of Anything?: The bringer of doom that invades the crystal of Wind is a multi-headed beast... Hmm...
- Hoist by His Own Petard: One of the easiest way to defeat him is to use a thief to steal two items from a head and use them on the other one.
- Power Nullifier: Water and Fire elemental attacks are this for him. Striking either head with an opposite-elemental attack prevents that head from using its powerful area of effect elemenetal breaths for three turns. If either head is powerless, the other cannot use Blazzard.
- Yin-Yang Bomb: The aforementioned Blazzard, which either head can use as long as both haven't been de-powered, douses the party with both fire and ice breath for devastating effect. Despite its appearance, it's actually Non-Elemental.
Rusalka, the Purveyor of Doom
The elemental beast that guards the Water Crystal.
- Achilles' Heel: Is weak against Lightning attacks, which is not really a surprise, considering she's made almost purely of water. This goes for its duplicates too.
- Samus Is a Girl: Not that you could tell looking at it, but she is female, according to the journal of D and the Slavic mythology.
- Self-Duplication: Can create 3 duplicates during the fight.
Chaugmar, the Mark of Doom
The strange and dangerous beast that guards the Fire Crystal.
- Achilles' Heel: Weak against Lightning attacks.
- Barrier Warrior: His entire strategy involves putting himself behind a force field that reduces the party's attacks to virtually nothing and detonating it for massive damage.
- Life Drain: Capable of draining HP, MP and BP.
- Loophole Abuse: His barrier works by increasing defense. Using attacks which ignore defense, or which deal set damage, can kill him before he even lowers it.
Gigas Lich, the Propagator of Doom
The undead beast that guards the Earth Crystal.
- Achilles' Heel: Is weak against Light attacks.
- Dishing Out Dirt: Knows the Quaga spell.
- No Cure for Evil: Averted. He's an undead, but he gets by this limitation by taking advantage of his elemental absorbance to Earth, by casting Quaga on himself.
- Our Liches Are Different: He's a giant.
- Revive Kills Zombie: Healing spells and items inflict damage on him. This makes White Mages and Salve-Makers especially useful against him. The aforementioned tactic of using revive to kill him, though, does not work as he will simply revive himself after being killed.
- Shout-Out: As mentioned above, to Lich of Final Fantasy I, that game's first fiend (as the four crystals of this game are awakened in the reverse order of that game).
- Standard Status Effects: Can inflict Fear and Death on your party.