Related
Effective Weapons
Members
As you might expect, Monsters of the Spellcaster family tend to cast Spells. The Rune Blade is effective against them, and unlike most family-killing Weapons, this one has a few very handy strengths. In particular, it's an excellent Weapon to use against Ogre Mages, as the accuracy bonus helps break through their evasion when they cast Blink Spells. It can also be a useful Weapon against Dark Wizards and the Evil Eye in the Ice Cavern, but beyond that point in the game, it loses a lot of its appeal.
Members
Astaroth, Beast Demon, Beelzebub, Death Rider, Devil Wolf, Ghost, Green Soul, Imp, Imperial Shadow, Iron Giant, Lamia, Lamia Queen, Magician, Mantis Devil, Mythril Golem, Ogre Mage, Pit Fiend, Red Soul, Roundworm, Salamander, Skull, Sorcerer, Specter, Stone Golem, Vampire Girl, Vampire Lady, Wizard, Wood Golem, Yellow Soul
The Spellcaster family is large, but you won't find any weapons that are powerful against them until the end of the game. On the upside, those weapons include two ultimate weapons of their type as well as the Excalibur. You can exploit this weakness pretty effectively if you pay attention, but by now you're likely doing enough damage that it doesn't really matter.