Fafnir/nidhogg can be extremely difficult or extremely easy to defeat depending on strategy. I will post some useful information and some tips and suggestions on strategy. We should discuss this and pool together our knowledge to develop the most efficient way to defeat him.
Positioning:
1. Breath Attack - The most important thing is positioning. What works best is tanks stand on his feet and mages and melee stand directly behind the tanks. His breath attack is cone shaped, so the further you stand back the more dmg you will take. The breath attack can one-shot anyone, mage, melee, or even a tank. Some people say melee can stand to his side. But considering his breath attack is cone shaped this could be tricky. One mistake in their positioning and they will take huge amounts dmg or even die.
2. Flail Spike - Once again positioning is everything. NEVER ever stand behind Fafnir or anywhere near the rear of him. This means THF can only TA on the tank and not use SA at all. If someone gets hate from behind Fafnir he will use Flail Spike and totally destroy the alliance. Unfortunately this also seems to be the best way to MPK someone fighting Fafnir, so a dishonorable LS may try and spam cure on the tank from behind Fafnir causing us to wipe.
MP Recovery:
This fight can drain mages on MP fast so having a MP recovery plan is important. Never ever use TOD spells on Fafnir. This is because it may become necessary to sleep him so that the alliance can recover MP and mages can catch up on healing. Fafnir can be slept fairly easily; however the biggest threat of doing so is someone stealing the claim. What works best is to cast non-DOT spells such as debuffs on him and for pld to alternate voking when he is asleep. This will prevent Fafnir from going unclaimed so that a LS can steal him.
Tanking:
NIN can tank Fafnir and it has been done before, however PLD is the most efficient tank for Fafnir for several reasons. Tanking with staff does work but considering this fight is all about hate control, PLD should tank with sword/shield. There should be a minimum of 3 PLD to tank Fafnir. 2 tanks are in same tank party and share hate as much as possible and this is why: Fafnir likes to spam terrorize, so each PLD should make a terrorize macro to inform the off-tank to take over tanking. The 2 PLD switch back and forth regularly when they become terrorized. If a PLD drops they should be kicked and backup tank invited in their place. However the backup tank will have a hard time getting hate, so the best solution is to not let the tank die ever under any circumstances.
Damage Dealers:
Since this battle is all about hate control dmg dealers need to be careful to not get hate. Hate will build over time sense this is a long battle (especially on Nidhogg). A common BLM strategy is to nuke as much as possible without getting hate, then log off and log back in to reset hate. This means there needs to be a party leader that is familiar with using the "/pcmd add" command. Blink is pretty much useless in this fight so some people say that rng should sub whm for Stoneskin; however I don’t think it is really that necessary. Also WHM can alternate being primary healer while the other rests for MP and or log out to reset hate.
The conical breath parameters are really just superstition, but may as well run with them. That being said, it'd be 'safe' to have all melees/mages in the yellow box, while being wary of being too far back. It's best to keep them on the side, near his frontal leg.
I find the most troublesome aspect of the battle to be Hurricane Wing. It causes quite a nice chunk of damage, so healing magic hate can be a problem. This is where SMN comes in. SMN is arguably one of the best classes for fafnir for one reason: Spring Water. If anyone says 'Earthen Ward' I'll slap them. There's no reason for it. Logic:
Spring Water 'cures' (Hatelessly) 47HP+3xLvl HP (272HP @lv75) AND removes the pesky Blind.
Earthen Ward 'cures' (As in, prevents, irrelevant) 50HP+2xLvl HP (200HP @Lv75) and doesn't prevent a status ailment.
Spring Water costs 7 more MP. But.. heals 72 more HP and removes blind. As you can see, it's obviously a superior choice. Making it MORE EFFECTIVE is the idea that some melees (RNGs) may be /WHM for stoneskin, which would negate Earthen Ward's usefulness.
Hope you find this guide usefull. Premium membership access |Yes please| =P
Edit: I made this for my LS also "We should discuss this and pool together our knowledge to develop the most efficient way to defeat him." is what I wrote on my linkshell. >.< bad move on me I guess. You probably didnt see this guide unless you have member access to website of LS.