I dont know about the other systems but the Conqueror is just unstoppable. He can block literally anything and stun you to the ground over and over again. And how is it that he can swing his ball and chain faster than I can swing the base attack for the Berseker!? Still a fantastic game just hope they consider fixing the Conqueror.
The character you're talking about is the conqueror, yes his chain attack can be annoying but just dodge or block it. As for being knocked to the ground try attacking him when you see the unblockable icon pop up. This will stop him and you'll get a free hit off, just make sure its a quick attack. Dodging this attack in my experience usually doesn't work as it has tracking. If you're having trouble fighting a certain class i recommend watching their "How to Fight" videos as these will better help you understand the mechanics of that particular class. You don't have to have the character unlocked to watch them just go to their class sheet under the "Heroes" tab.