Zable Fahr is the God-Beast of Darkness. It appears as a boss in Seiken Densetsu 3, and it takes the form of three disembodied heads, only one of which contains the boss's main life force. Though it is assumed to be sentient, Zable Fahr doesn't display any personality aside from a desire or instinct for destruction, at least until a side-quest to visit it as a Benevodon in Children of Mana.
Zable Fahr was described as being an "incarnation of disaster" that existed before the world had been fully born. It reigned destruction on existence until the Goddess of Mana defeated it with the Sword of Mana and sealed it away inside the Mana Stone of Darkness. At some point later, the Dark Prince tried to summon the Mana Stone of Darkness before the Goddess of Mana sealed him away in the Underworld.
When the villains in Seiken Denestsu 3 obtain the Sword of Mana, they release the God-Beasts from the Mana Stones. Zable Fahr isn't released at the same time as the others, however. After the other seven God-Beasts are killed, the heroes must travel to Pedda in order to learn Zable Fahr's location, which changes depending on which character is the main protagonist. In Duran/Angela's story, Zable Fahr is in the Glass Desert, in Kevin/Charlotte's story, it is in the Jungle of Illusion, and in Hawkeye/Riesz's story, it is in the Cave of Darkness. Regardless of its location, Zable Fahr is released just as the heroes discover the Mana Stone, and although it proves a deadly foe, the heroes still emerge victorious. After its death, Zable Fahr's power was sent to the Sword of Mana like all of the other God-Beasts.
Zable Fahr is generally viewed as being the most difficult of the benevodons to defeat (despite the characters usually getting their 2nd class change before fighting it), as well as the one of the hardest bosses in the game. In the first part of the battle, the heroes are drawn into a strange, void-like arena where they are attacked by two humanoid heads, each with over 5,000 HP. The attacks they use are somewhat weak compared to the attacks used by some of the monsters in the dungeon leading up to the fight, but most of them affect the characters' stats. After the heroes kill the two heads, a third, almost feminine head appears and revives the other two heads, marking the start of the battle's second phase. The main head has around 10,000 HP, but since the two weaker heads must be killed to make it appear, Zable Fahr technically has around 20,000.
Once its main head joins the battle, Zable Fahr will begin using its most powerful attacks such as Hell Cross (an extremely powerful Darkness-element attack), Dark Force, and Death Spell. As the heroes are unlikely to have reached a higher level than the boss, Death Spell will almost certainly be fatal. The combination of Zable Fahr's attacks and the stat-reducing attacks of the extra two heads can also be very deadly. Although the two weaker heads can be killed again, the main head will soon revive them; if the main head is killed, the weaker heads will die along with it.
Being a Darkness-elemental entity, it's weak against Light-based attacks and magic. It's also healed by Darkness-based attacks and magic.
Flame Radiation (one) - Left head only
Tongue Attack (one) - Left head only
Darkness Beam (one) - Left head only
Gremlin (one) - Level 2 summon
Great Demon (one) - Level 2 summon
Demon Breath (all) - Moderate magical damage; left head only; lowers magic effectiveness/resistance; casts at 1/4 HP
Evil Gate (all) - Level 1 Dark magic; right head only; used to heal self if at 1/4 HP
Dark Force (all) - Level 2 Dark magic; right head only
AntiMagic (all) - Negate's targets status and elemental sabres; right head only
Death Spell (one) - Instantly kill a single target if below caster's level
Black Curse (one) - Lowers all stats of specified target
Hell Cross (all) - Heavy magical damage; can only be used when all three heads are present
Dark Blazon (one) - Moderate physical damage
Darkness Beam (one) - Moderate magical damage; lowers target's magic effectiveness/resistance
Regeneration - Revives other two heads