First off you have to feign split 5 reavers to kill them all and get Lord Rak'ashiir to spawn. Second, the only 2 things on this guys Sh*t list should be 49+ warrior type mage fire pets and the clerics healing them.
Spells this guy casts:
Gravity flux
Complete heal (serious, saw it once)
Immolate (2000dmg AE 0.5 second casting proc)
And various other wizard spells appropriate for this guy's level. You need to kill this guy close to where he spawned from the last reaver so that he doesn't gate when he get's low.
This guy has almost as high resists as a black reaver but a few lvl 60s that tash and malo him might be able to eventually get off a slow with help from call of hero to wipe their agro after a spell lands.
Dump tons of buffs on the fire pets and have your shaman turn in the iksar child tear and he will respawn as agro and attack the shaman. I think he only drops the 'scale' for the shaman epic quest when you kill him after turning in the tear so you should probably make sure to do everything else in your epic quest before doing this part. He might give you the scale before agroing though, that part is unclear to me.
This is the last guy for the shaman epic quest and is equally challenging. Typical levels that should try for this guy should be in the lvl 55 range like all other epic quest mobs.
Anyway, remember that you have to kill 6 different reaver spawns, ghiosk, and this guy and you should be fine. I wouldn't even attempt going after this guy without like 12 or so lvl 55+ guys.
This guy drops the atrementous shield as rare, and ornate rune blade as common. I think he drops lvl 55+ spells too but not common enough to bother killing him if you don't have a shaman doing their epic with an iksar child tear in hand.
Good luck shamans, just wanted to help you out =)