NOTORIOUS MONSTER WEAKNESSESEvery Abyssea NM is weak to one physical WS, one elemental WS, and one spell/song, and triggering each weakness causes a "!!" to show up on the mob, seals some abilities for a short time and forces it to drop more loot. Each weakness is randomly selected from a list of possible ones at the time the NM is claimed/spawned. A detailed explanation, as well as the list of possible weaknesses, is located
here.
The three types of weaknesses are as follows:
Red: Inflicts the Terror status, totally immobilizing the NM for 25 seconds. Triggering the Red weakness forces the NM to drop all potential key items, including pop items (though only to the person who claimed it), Abyssites, and Atma. Pops and Abyssites have a not inconsiderable chance to drop without Red triggers, but Red is the only way to get an Atma to drop. It's triggered by one of 13 possible elemental weapon skills, the selection of which is totally random as far as anyone can tell. Notably, however, a WAR and a NIN with properly-leveled combat skills and enough time can cover all 13 between the two of them.
Blue: Inflicts Amnesia for 25 seconds, preventing the use of any TP abilities. Blue !! raises the possibility of the NM dropping any unique weapon or armor drops to around 80%; you'll usually go for it when hunting for a particular accessory or something. It's probably the hardest to trigger, because it's triggered by a physical WS, of which there are 3 groups of 15 possible. The particular group is determined by the time of day you pop/claim; 23:00 to 7:00 is Blunt, 7:00 to 14:00 is Piercing, and 14:00 to 23:00 is Slashing. As you can see, you usually need a bunch of classes to land Blue, though notably one of the best things about the MNK + WHM duo is that they can hit all possible Blue triggers if they claim during Blunt time.
Yellow: Inflicts Silence for 25 seconds. Yellow !! increases the number of class-specific upgrade items a given mob drops. Without Yellow !!, for instance, Tier 1 NMs drop 0-2 seals; with Yellow, they drop 4-5. It's triggered by spells; the specific spell will be determined from the list in my link based on the day of the week you pop/claim. It will be either the element of that day, the day before, or the day after. For instance, if you claim on Windsday, the Yellow trigger will be wind, water, or ice.
The drop benefit is negated if you trigger the same weakness more than once on the same NM, but they don't, as far as anyone can tell, affect other weakness pops. So if you want an Atma from an NM and don't care about anything else, you can chain Silence him by continuously proccing the Yellow weakness, though they do build resistance and the durations get shorter.
Basically, the idea here is to incentivize bringing more people so that you can trigger weaknesses and get more loot. Though I personally can solo most tier 1 NMs, for instance, if I want seals, I'd consider it a waste of time to go farm them without a BLM or BLU in tow to help trigger Yellow; ideally I bring someone who wants different seals, but even if there's a conflict, the difference between proccing yellow and not proccing it is so big that I'm still ahead of where I would have been alone.
