So I've heard the differences on a couple of the fights but it would probably be good to assemble a list.
Halfus I have as all drakes and abilities are available. Magmaw I have Bone constructs being thrown out that leave very deadly fire trails that crawl till 30% at which time nef stops throwing bone constructs and starts lobbing aoe bursting shadow bolts at random people. Chimaeron the best I can see is that he still melees and double attacks during feud and he has a shadow aura ticking on people in the last phase.
All in all, all of the heroic fights are just that much more difficult and of course the recent patch notes nerfed some of the boss abilities. If I'm correct, there's only the red, blue and green vials for Maloriak still. No black vial. That'd confuse too many people who aren't paying attention.