Went with a 60, and 74 Mnk, and they were totally trashing the Dark Spark until it self destructed and took out 3/4 of mine (53 Pld) and the 60 mnks hp. The 74 Mnk was kind of upset because he hit the wrong macro and didn't get to do Ashuran Fists on it. I think the 60 mnk wasn't subbing nin though and I was subbing whm for sneak/invis. He went down a lot faster then most exp mobs I have lvld on. Hardest part of the quest was getting to the coffer
I am working on getting Monk AF gloves. Do I have to get the Crawlers Nest coffer before I fight Dark Spark for the flames? Will I get the key Item fame If I kill Dark Spark before getting the coffer?
I can confirm that you must open your respective coffer, talk to Guslam (Upper Jeuno), talk to Yin Pocanakhu in Tenshodo (Lower Jeuno), and examine the toolbox in Port Jeuno. Only after doing all of this will you be flagged to receive the Shadow Flames after killing Dark Spark.
I helped kill him in an alliance after doing Genkai 2 and did not get the Shadow Flames (i had not found the coffer key yet at the time). Hope this helps.