Natures are creature types which are used to determine a weapon's or spell's possible effect on the target. Natures are typically fixed; they can never be removed and can never be set with the exception of the Dragon's Kiss attack, a Mix coming from a Dragon Fang and a Maiden's Kiss, which sets both the Heavy and Dragon nature on a target.
Note that Undead has nothing to do with elemental properties; they are often put together on enemies and the Bone Mail, but inherently they have nothing to do with each other. Creatures with an Undead nature invert the effects of draining spells, are damaged by curative spells and items but are fully restored by the Death spell and linked attacks. Those with an Undead nature:
- Gain HP by those attacks which drain HP and/or MP: damage is dealt to the caster instead.
- Normal restorative attacks and items damage instead of heal with the sole exception of White Wind.
- Restorative attacks and items that normally restore HP back to full instead reduce the target's current HP to a single digit. This is not the case when the creature also has a Heavy nature, in which case the attack does nothing.
- Death, Death Potions, Level 5 Death and Roulette restore the target's HP back to full instead of setting Death.
- Reviving attacks and items set Death when cast on Undead creatures; when the Death status is set, these attacks and items will not revive them. This is not the case when the creature also has a Heavy nature, in which case the attack does nothing.
- Takes damage from the Requiem Song. This song has no effect on creatures without the Undead nature.
- The Sage's Staff and the spell used by Apollo's Harp deals eight times as much damage.
Heavy can be described as a quality which grants resistance to all kinds of instant-death effects and other debilitating properties that do not include the actual Death status immunity bit. "Bosses" and the Heavy nature often go hand in hand, but not always; certain random encounters possess the Heavy nature, and certain bosses lack it. The term "Heavy" is not an official term, and you'll note that this nature is the only one not mentioned in the Bestiary. A Heavy nature allows the creature to circumvent:
- Immediate destruction at the hands of Bio, Firaga, Blizzaga, Thundaga and Holy Spellblade effects when the target is weak to said element.
- The effects of !Flirt and the Lilith Rod.
- Percentage-based attacks such as Graviga, spells used by all Harps (but not Apollo's Harp), Missile, Level 4 Graviga, etc.
- Attacks which reduce the current HP total to that of a single digit, such as Dark Elixir, Tailscrew, Death Claw, etc.
- For those that also have an Undead nature, destruction at the hands of reviving items and spells, reduction of current HP to a single digit at the hands of Curaga, Elixir, X-Potion, Transfusion and Embrace.
- Destruction attacks and spells such as Odin's Zantetsuken, Banish and !Iainuki.
- Death by countdown such as inflicted by the Blue Doom spell.
- The results of !Condemn.
- Being forcefully removed from the battlefield by Encircle or Possess - The effects of Grand Cross.
- Status ailments set that have a timer such as Stop, Paralyze, Sap and Silence will have a sharply reduced time of effect; about 25% of the time a normal character takes to charge his/her ATB bar.
The Magic Beast nature is just there to check for a certain type of creature for the purposes of certain attacks.
- The Beastmaster's !Calm command was supposed to set Stop only on creatures with a Magic Beast nature; instead, it can set Stop on all targets except for Magic Beasts.
- The Artemis Bow and the Beast Killer Whip deal twice as much damage to creatures with a Magic Beast nature.
The Dragon Lance and Dragon Whisker deal twice as much damage to creatures with a Dragon nature. The spell used by Apollo's Harp deals eight times as much damage. The !Combine attacks Dragon Shot, Dragon Burst and Dragon Cannon all deal twice as much damage.
Aqua Breath deals eight times as much damage to creatures with a Desert nature. These include every creature that can be only encountered in the desert, with the inclusion of the Sandworm and the exclusion of Dhorme Chimera, Ankheg and Ammonite for whatever reason.