In my experience, all the BCNM's are really easy on Difficult and lower. My group always consists of PLD, WHM, BRD (2-boxed), DD x 2. 6th person doesn't matter. Can be a third DD or a 2nd bard or you can just go with 5.
- PLD rounds up everything, DD's pick off one at a time starting with BLM if there is one.
- Accuracy starts to be an issue on Difficult. With Verethragna 119, my monk needs sushi + accuracy gear if I'm not getting any accuracy buffs. Sushi + full DD gear if I'm getting double Madrigals. On BST, using Kerehcatl, either you or your pet are going to have accuracy probs. Although, I didn't have Totemic gear last time I did it on BST, so maybe I'll have to try it again. No Drachen Roll either way so my pet is going to have probs regardless.
- Make sure your DD equip full PDT gear when attacking RNG mob.
- You want your PLD to target MNK mob and try to get it to use 100 fists before your DD get on it. If no MNK mob, try to get PLD mob to use Invincible or THF to use Perfect Dodge.
- If you have a SMN mob, always do it last and have Scherzo up before engaging it.
- If you are doing the one with a BST, make sure to do him last and either block charm with Fealty/Asylum, or be ready to sleep the charmed person.
- WHM mob will use Benediction so either target it first or last so it doesn't heal other mobs for much.
I've done all the SKCNMs multiple times (enough to get chapters for 109 AF and 109 Relic for 6 different jobs). In Den of Rancor, I prefer fighting Sahagins over Tonberries. In Fei'Yin I prefer Gigas over Fomor. For Chapter 5's, I think we always did Orcs because Hurlbat sells for a lot. But they probably aren't the easiest.
That's pretty much all I can think of right now.