Final Fantasy IV enemy types

Dragon
Dmg*4
 * Dragoon Lance
 * Dragon Whip
 * Artemis Arrow
 * Tiara
 * Dragoon Glove
 * Crystal Glove

Dmg/4
 * Dragoon Shield
 * Dragoon Helmet
 * Dragoon Chestplate

Machine
Hammers are strong against Machines.

Dmg*4
 * Thunder Claw
 * Silver Hammer
 * Earth Hammer
 * Wooden Hammer
 * Lit Arrow

Reptile
Dmg*4
 * Ice Rod

Dmg/4 Ice Shield

Spirit
Mythril equipment oppose spirits.

Dmg*4
 * Ancient Sword
 * White Lance
 * Silver Knife
 * Silver Dagger(?)
 * Silver Hammer
 * White Arrow
 * Silver Chestplate
 * Silver Ring

Dmg/4
 * Silver Shield
 * Silver Helmet
 * White Cloth
 * Silver Glove

Giant
Dmg*4
 * Charm Claw
 * Drain Sword
 * Drain Lance
 * Ogre Whip
 * Poison Axe
 * Charm Arrow

Dmg/4
 * Zeus Glove

Slime
Drain equipment oppose Slime enemies.

Dmg*4
 * Drain Sword
 * Drain Lance

Mage
Dmg*4
 * Silence Staff
 * Mute Dagger
 * Rune Axe
 * Elven Bow
 * Mute Arrow

Dmg/4
 * Aegis Shield
 * Ribbon
 * Rune Glove

Undead
Crystal and Paladin oppose Undead enemies. Drain equipment do too, however this heals the opponent four times as much, and damages the player that same amount.

Dmgx4
 * Lilith Staff
 * Silver Staff
 * Drain Sword
 * Drain Lance
 * Crystal Sword
 * Dummy
 * White Arrow

Dmg/4
 * Paladin Shield
 * Crystal Shield
 * Paladin Helmet
 * Crystal Helmet
 * Wizard Cap
 * Paladin Chestplate
 * Crystal Chestplate
 * Sorcerer Cloth
 * White Cloth
 * Paladin Glove
 * Crystal Glove