theres another topic on this you may wanna read, has some good tips. if you kite him to the room right next to moroes room (where the people dance) you can position your shamans on the room ABOVE hanging out on one of the pillars - the other thread has a screenshot. The red bubbles won't hit your ranged DPS, so you just have to kite him with your tank then and pew pew/heal with the others.

However imo this still is exxxxtremely tedious with just 5 people. I tried it 4-5 times and couldn't get him below 25% after 20-30 mins, he'd heal up constantly and eventually my shamans ran oom. I instead just spamm'd shattrah "lfm 5 more dps/healers (axe reserved) new karazhan boss ONLY", summoned them, had everyone stand where my shamans were, and we killed the boss in under a minute (chain heal through damage on all shamans). Was a ton easier than trying to solo it