This category contains monsters that appear much more rarely than normal or under special conditions. They are generally more powerful than other monsters of the same type. They can be identified by a purple check icon with a question mark on it ("Impossible to gauge!")
Notorious monsters often drop unique or otherwise rare or hard-to-find items in line with their greater difficulty.
There are different types of notorious monsters, or "NMs:"
Timed spawn NM
These are NMs that appear normally in the game world like regular monsters; however they typically take longer to appear and only one appears at a time. They might also only spawn at certain times of day or with other conditions attached.
All NMs have a "rage" timer. After a period of 30 minutes has passed since the target was engaged in combat, its strength will increase over time at an exponential rate until the fight ends.
Faction Leve NM
These NMs are bosses for special Faction levequests.
These are typically bosses in a storyline quest. They appear in special areas or within an instance only accessible by you and/or your party members. When entering one of these fights, you will be asked beforehand, "Duty calls. Would you like to proceed?" If the battlefield was part of a quest or storyline and you fail to defeat the NM(s) or you are disconnected, you can generally start the fight again by re-approaching the entry point.