- hunter pets (including stampede);
- unholy dk ghouls;
- priest mindbenders (and I assume shadowfiends, though none of our priests were using them);
- shaman elementals (fire and earth).
Now, the list of things that did not get fully mutated:
- monk Xuen;
- unholy dk gargoyle;
- dk army of the dead;
- blood dk dancing rune weapon;
- warlock doomguard (our locks were using GoSac, so can't really say about other demons yet);
- mage mirror images;
- shadow priest shadowy apparitions;
- paladin guardians of ancient kings;
- shaman spirit wolves and damaging totems.
I'm sure there's some stuff that I missed here, but that's already quite a list of things that have their power reduced by 75% on this encounter. I'll admit that the boss is absolutely killable without all these creatures doing full damage on him. However, for any guild still struggling to down Primordius, either on normal or on heroic, this might be a sizable hurdle to overcome.