Some more ideas for Beastmen troops, somewhat on elites. and most importantly specials.
Bovigors
Change from my first post. Perhaps change the Bovigors from having mail and shields to simply being armed with a mace or spiked club, possibly aslo a shield and let them bludgeon the heroes without much armour to protect the Bovigors.
I got my lore wrong and it seems these guys are stronger and dumber than the average Beastmen so they probably shouldn’t get something as fancy as armour.
Elites
Foe-render and Halfhorn
Provide upgraded versions of Gors into an elite status to represent small group leaders called “Foe-render” for the Gors and “Halfhorn” for the Ungors. I imagine these could be a bit larger than the normal versions of their respective enemy, more impressive horns and perhaps some cool Chaos runes tattoos to make them stand out from the common troops?
Quadrupedal enemies
Something which I have been thinking about is four-legged enemies. The great problem with this is getting on and off different heights. But I personally wonder if the animation for this couldn’t be to let them make a leap that takes their fore limbs over the edge and they then pull themselves up?
The risk is that it might look odd but if anytone would figure it out it would be the people over at Fatshark. 
Centigor
Centigors could be armed with a hand weapon or a spear, and perhaps some of them with a shield, and come charging which means that they would be similar to the Bestigors but without the armour but probably with some faster attacks but also present a larger target and constantly faster movement.
Chaos Hounds (as a form of infantry-special)
These could also be added to the Rotbloods and work like an assassin which can only make a short leap forward but takes a bit more beating to put down, and naturally will come running over the ground without the ninja-moves.
Specials
I’ve gone through the “Tome of Corruption” with its list for mutations associated with Nurgle and also the “Gifts of Nurgle” list for suitable ideas.
I didn’t get together as many ideas as I thought but here are a few. I figure that the Bray-Shamans can perhaps act as the non-warrior specialists while other specialists are a bit tougher Beastmen warriors with some special effect?
Boilgor - Works like a bit tougher Gor, with several big boils, but when struck there’s a 0,3-0,5 seconds delay before there’s a gush of dark green acid in the direction from where the attack was launched. Being hit gives acid damage. Thus forcing the characters to keep moving or get into trouble.
Vomit Beast - A Gor with a swollen body, walks a bit slower than the normal Gors, and can vomit over a piece of terrain to cause heavy acid damage on anyone walking over it and so act as an area denier.
Plague Beast - A Beastman warrior who has a chiming bell with him. He can both attack with his weapon and spread his plague around him. But the effect is the same. The hero will get a curse that lasts for a time. I am not terribly sure about the effects for this one but something similar to the Grail Knight blessing but in reverse seems likely. Thus acting as both an area denier and also a debuffer/curser on the heroes.
Mask of Decay - A Gor with a iron mask-helmet over his face. When close to the characters he gives a roar and then his eyes turn into an intense clear green and any hero close by are affected by the same kind of visual effects we call love from the end event in Convocation.