Sooo, I have specced to combat because I was lucky to get 2 heroic axes and 4pcs T15. I was excited to try it because of the change after about year of spamming mutilate. But for real, nothing changed, killing spree is still stupid.
I have tried almost every HC boss except Lei shen. So there are my findings:
Jin'rokh - don't use it while lighting storm, you will probably die
Horridon - killing spree on adds, sometimes it jumps to the boss during double swipe. Soooooo awesome! you will probably die
Council - Sand traps, Frostbite. if you do it in bad time, you will probably die
Tortos - not so broken here. When you killing spree you will jump under the boss and you are save here. (I think) you will probably not die here!
Megaera - I would say lol. Don't use it here. It's useless and stupid. When you try to killing spree living head it will jump to the place where isn't head! so, you will do nothing, just watching your character jumping in front of nothing. You will probably not die, but your face will be like... WTF I've just done.
Ji-kun - not good idea to use killing spree during nest where big add needs to be tanked. You can jump in front of him and die.
Durumu - killing spree during maze = death
Primordius - killing spree jumping all over the room, sometimes it jumps down to the stair where is way to the Ra-den. You'll see what others can't. Coool
Dark Animus- ehm, you know... jumping everywhere around the room.
Iron Qon - I think one and only boss of instance where you probably can't die. Except one thing - when under boss is fire or frost line (I don't know name of ability). You can die.
Twin Consorts - Jumping from ice coment to ice coment and to the boss and then .... bleh.
grammar nazis- come at me, I am from czech rep. :P