I merc these NM's, so here are my general strats. Of note I do not have heavy caster jobs, I'm THF, COR or RUN and my GEO alt.
Belphegor (Corse) - I go COR or RUN and savage blade. My GEO melee's and hexa strikes to open light. I do my best to let Amchuchu tank because of the charm.
Crom Dubh (Dullahan) - Two strategies: If you have a "real" tank, Aegis PLD or just a RUN in solid DT, COR wildfire or any nuke setup is perfectly fine.
If you want to bring melee, I've had success using MDB buffs. Magus roll and Indi-fend allowed me to melee on COR and wildfire it, trusts still occasionally died but my characters survived. Maybe adding on Indi-fade would make things safer as my GEO has an Idris.
Dazzling Dolores (Morbol) - Blink tank, light SC / fire damage. For an easy clear I go RUN/NIN DD, vex/frailty from my GEO, melee on geo to open light for savage blade. Dolores levels up when it "heals", and you can blink lashes and avoid dealing darkness damage to it rather easily. Fire damage will reset level ups if you're an idiot and keep Arciela on as a trust from a previous kill.
Golden Kist (Mimic) - MAGIC EVASION. I use Runeists roll on COR, sometimes have my GEO come /whm to barpoison. As soon as it pops I indi-attunement. Usually attunement + runeists let me fully evade death trap. That takes care of the first major issue. The 2nd issue is zombie aura. Malaise from my GEO, and use the correct QD shot from COR and nukes on GEO usually has no issue resetting in time. You're going to have a bad time if you aren't avoiding death trap and dealing with zombie though, so MAGIC EVASION.
Kabandha (Ahriman) - Back tank, otherwise he's annoying but easy.
Mauve-wristed Gomberry (Tomberry) - When I dualbox it now I utilize two tanks and go as COR. Wildfire spam to keep my hate low and keep hate on my trust tanks. If you're doing this as a full group you need your tanks to reset tonberry hate, but trust tanks have no tonberry hate as a default so lets you get around that. This is another one where magic evasion is huge, so runeists + attunement. Barblizzara and barparalyzra to avoid para/bind. My GEO nukes and generally one -ra 3 resets, but I usually cast two to be safe as it has some weird resistance I haven't yet figured out sometimes.
Oryx (Monoceros) - Can't use GEO debuffs, barthunder + barpara + indi-attunement to keep para/silence landing and keep tp moves from owning you. Try using crit WS from the front to break horn but it's so irregular just accept it's going to be a slow fight.
Sabotender Royal (Sabotender) - You need to either be able to burn it down quickly below 40-50% or accept your tank is going to die if you need some more time. I'd say this is probably the hardest one for new groups to get down because it's the tightest DPS race, the rest of the fights can be more controlled and longer, but ??? needles is no joke. If I want to be 100% certain of winning I bring my COR friend and go as THF. Malaise/frailty with Rudra > Leaden > Rudra usually destroys it. And if not, the COR is at range to finish it off after ??? needles gets me. Always have reraise though...always.
Sang Buaya (Bugard) - Silence and win. This can be hard though as I often need to bring out focus/languor to land it on my GEO, so alternatively I'd try barthunder + attunement to avoid the stuns. He takes magic damage perfectly fine, so a regular SC+MB strat is probably ideal as I think you also outrange the stun too.
Selkit (Scorpion) - Have multiple people capable of taking damage. DT works with Hell scissors, so maybe a double PLD setup, otherwise just burn it. The faster you kill it the less likely it'll get his more annoying tp moves off.
Taelmoth the Diremaw (Soulflayer) - Pure melee setup. PLD aegis tank during Azure Lore can probably/hopefully survive and have melee run out during it in case it tries to AOE. Otherwise pure attack buffs and burn it. Barblizzara for spectral floe though.
Zduhac (Greater Bird) - Never had an issue, but I'm a THF and big birds are my forte. I just burn it down, but might need attunement if not geared for that.