Where Two Paths Converge

Checklist

• Get mission from guards.
  
• Talk to Karst.
  
• Talk to Cornelia.
  
• BCNM (uncapped) in the Throne room (same place as shadowlord).
  
• Talk to Karst.
  
• Talk to Cornelia.
  
• /dance, /joy, /hurray!
  

BCNM: Whoo boy, I really can't recommend this if you're below 70. We were 68-75 and the 68's had a bit of trouble.
They say you need a Blm. This is simply untrue. We were able to beat this with our "weakest" team: 75Pld, 72Whm, 72Rdm, 62Pld, 68Rng, 68Thf. We really just barely squeezed that one out, with 3 deaths. We were only able to get around not having a Blm by using paladin's 2hr, invincible.
Ok so here's what we did: Beat on Zeid but save your TP. Do your very best to conserve MP during the early fight, you'll need a ton of healing later on. Approximately 1/4 through his HP there will be a cutscene and Volker will join the fight. You might want to use poison potions here, because "shockwave" can put you to sleep, but in 5 attempts (3 successful) we only had this occur once. About 30 seconds after the cutscene, Volker will attack Zeid - you cannot stall this by having someone remain inside the cutscene. Designate one of the healers (whm usually) to keep Volker alive, because you lose if he dies.
Make the "Light" lvl3 skillchain as often as you can after the cutscene. Have all melees concentrate on Zeid. Zeid will then create two shadow images of himself. This is when the paladin uses invincible. If you do not, the shadows will end up on Volker or the mages, and that's death. They deal a lot of damage so the no-damage taking part of invincible is really nice too.
If you have a Blm, Sleepga II saves the day here in place of invincible. A big -ga spell can often wipe the shadows in a single hit.
Without a Blm, a Rdm can use Fire III and Aero III to kill the shadows.
I believe this becomes an easy fight with a standard all-75 Pld,Whm,Blm,X,X,X party. For me it was a lot of fun trying to beat the odds, however.