Theres a jumping attack, that continuasly chain to ppl withing 3 yards of the originating target, dealing double damage each time it jumps, and I believe that after a certain number of jumps (3?) itll jump back to the same target, meaning if you are stacked up past 2-3 ppl, they will get instagibbed. It's also casted constantly on multiple targets
So, a faction just rushing this without any planning will most likely quickly wipe. A wandering player jumping in to get the loot will be responsible for his own healing. A group of griefers can easily wipe an entire raid with proper positioning. On the other hand, it seems that if you get the spreading part done, its mostly a tank/spank with emphasis on the tanking, since tanks have to swap AND they can't taunt.
DBM /range 5, make sure radar is green for the entire fight. Anyone that's killed Feng on normal mode should know what to do.
The chaining fire damage is the anti-zerg ability. If a raid group is properly spread, he can cast that spell all day and it won't do much of anything. But if you bring in 200+ people to the fight and /can't/ spread out, it's going to be killing 15 people every single cast until it's thinned things down. The whole boss is a coordination check, I think the reason that they mention 'multiple heroic raid groups' is because if you're a 10 man guild you won't have the raw DPS to do it without teaming up with a second similarly skilled 10 man. Not because they expect it to be fought with 100+ heroic raiders.