Serberys Raiders
"We already know how great Skitarii are, but you know what would make them even better? If they rode cyber-beasts into battle! And if some of those mechanical quadrupeds also breathe fire?!"
- – Men of culture at Warhammer community
The Serberys Raiders are new Adeptus Mechanicus units shown off at Las Vegas. Looking like Krieg rough riders, but with robot horses/dogs that breathe fire, they look absolutely awesome. They have two options from what I can tell, a robot horse that looks awesome and a robot dog that looks almost as cool, but well makes up for it by having a flamethrower as a mouth
That's all I can scrape together from the two sentences about these guys.