Aggro

Category:Terminology
Aggro is a shortening of "Aggressive (behavior)." This term refers to the behavior of an enemy approaching and attacking, as opposed to you attacking first.
Only enemies high enough in level, relative to your main job level, can be aggressive towards you (with the exception of Spheroids and some Notorious Monsters). Checking (/check) the monster can give you an idea of its level in relation to yours. Monsters that check as "Too Weak" will generally not be aggressive, along with some monsters in the "Easy Prey" range. However, Notorious Monsters will always check as "Impossible to Gauge", regardless of whether they are high enough in level to be aggressive towards you or not.
From level 71 (possibly 70) onwards, monster spawns with a level range reaching 61+ will continue to aggro up to and including level 99. This is irrespective of the particular monster's level; a level 59 monster in a 59-61 range spawn will aggro, but a level 60 in a 58-60 won't. No new level ranges become "Too Weak" after level 75.
Resting (/heal) temporarily drops your "level" to 1 as far as aggro rules are concerned. Meaning, if you rest in a "Too Weak" mob's aggro range, it will still aggro you no matter how high your actual level may be.
Most Beastmen aggro. Many higher-level enemies of families that do not aggro at lower levels may aggro as well.
Also note that although aggression is closely related to enmity, they are not the same. An aggressive enemy will attack without provocation, but until the player performs an action to generate enmity, it will remain at zero. Though this is usually a matter of technicalities, in some cases in can be relevant since, for example, enmity will not be generated by healing a character who has been aggroed but has not performed any action against the enemy. 
=== Methods of Detection ===
Enemies that aggro rely on one or several "senses" of detection, depending on enemy and type of enemy. What each enemy aggros to is typically noted within each Bestiary entry on this Wiki.
Possible methods of detection are as follows:
* Sight: The enemy will detect you if you are within 15 yalms, inside the enemy's "field of vision," and not Invisible.
:* This "field of vision" is approximately 60-75 degrees from the direct front of the enemy, and can be avoided by walking around or behind the field (and the enemy itself).
:* The faint inner circle on the radar is at about 15 yalms.
* Sound: The enemy will detect you if you are within 8 yalms of it and not Sneaked.
:* Sound aggro is detected in a circular radius from the center of the enemy's model. As such, walking behind the enemy will not avoid aggro to sound.
:* The Ninja Job Trait Stealth and the Ranger Job Trait Alertness can occasionally reduce detection to sound-aggroing enemies.
* Magic: The enemy will detect you if magic is cast within 20 yalms of it (counted from where you are standing; the position of the target does not matter).
:* Magic aggro is detected in a circular radius from the center of the enemy's model.
:* Spells that do not cost MP will not cause magic aggro. As such, Ninjutsu and Bard songs are safe to use.
:* The outer circle on the (non-Ninja) radar is at about 20 yalms.
* Ability: The enemy will detect you if you use a Job Ability or Weapon Skill within 20 yalms of it.
:* Ability aggro is detected in a circular radius from the center of the enemy's model.
:* At the moment, only certain monster families from Aht Urhgan regions exhibit this behavior.
* Low HP/"Blood": The enemy will detect you if your HP color is yellow, orange, or red while within 20 yalms of it.
:* Blood aggro is detected in a circular radius from the center of the enemy's model.
* True Sight: A version of Sight aggro that ignores Invisible status. (All other conditions of Sight aggro will apply.)
* True Sound: A version of Sound aggro that ignores Sneak status. (All other conditions of Sound aggro will apply.)
*Sleeping Non-Aggro: Some mobs in Treasures of Aht Urhgan and Abyssea areas are Diurnal or Nocturnal, and will therefore occasionally be sleeping. The "Zzz"s floating from their heads indicate that they will not aggro until they are awoken (either because they are attacked or because the clock changes to their "awake" time). Unlike normal Sleep, any type of aggressive action will cause them to awaken from this type of sleep, even if it does not deal any damage.
*Spawned Monsters: Many spawned monsters will immediately attack the person who caused the monster to spawn. In some cases, it may be possible to spawn the monster(s) with a Sneak effect up and cause the monster(s) to spawn passive (not aggressive). (Spawning monsters with an Invisible effect up is generally impossible because it prevents you from examining/trading to ???s or similar points.)
In nearly all cases, even if a monster is within range to be aggroed, aggro can be prevented by positioning yourself behind a wall or some other type of solid terrain, such that there is no clear unobstructed line between you and the mob (or the mob's line of sight, in the case of sight aggro). In other words, even if a magic aggro mob is 10' away from you, as long as you are behind a solid obstruction, you may still cast without aggro. Note however, that doors or gates (such as the Banishing Gates in Garlaige Citadel) do not count as valid obstructions -- mobs can see and aggro right through such objects as if they were not there. Furthermore, solid obstructions will not prevent magic aggro from True Sight and True Hearing enemies such as the Soulflayer.
=== Methods of Pursuit ===
Many enemies pursue their target (in addition to their detection methods) using Scent. It is possible to "lose" aggro on these types of enemies if the player Deodorizes him or herself while he or she is out of the enemy's widest detection range. If aggro was successfully lost, the enemy will give up chasing the player at the point where Deodorize was applied.
*Water element (Rain) weather and walking through bodies of water will have a similar effect to that of Deodorize.
See also: Link