For starters, in addition to Blackhand himself at the end of Blackrock Foundry, we have a surprising first boss for the raid - Gruul the Dragonkiller himself. He appears to be in the process of being converted into one of the infamous gronn siege tanks, or perhaps fighting free from said process - some of the abilities from the fight will be familiar, while others (Inferno Slice) are new.
Of course we have Blackhand at the end of the Foundry. What's interesting in terms of bosses we might not have expected is that Kargath Bladefist makes an appearance in the Highmaul raid. He's listed as the first
boss of Highmaul, in fact.
Kargath Bladefist, Chieftain of the Shattered Hand, honed his brutal skills as a slave in the Ogre's gladiatorial games. He slaughtered countless opponents for the promise of freedom, but after winning, was locked away with the other retired "champions". Fueled by rage, Kargath tore off his own hand to escape and led a revolt that soaked Draenor in Ogre Blood. Now, he eagerly returns to the arena to teach you the true meaning of savagery.
Seeing Kargath in the Highmaul raid and seeing the mention of him returning to the arena implies that the raid either contains an arena fight (one that Kargath participates in) or is one. I wonder if the Highmaul raid is situated to the north of Nagrand, either in the Warmaul or Laughing Skull regions we see in Outland.
At any rate, having Kargath, Blackhand and
Gruul popping up in the first tier of raiding is pretty interesting.