Is There Any Mechanism to Shun a Bad Actor or a Bad Node?

I don't think we have anything implemented currently, but we could implement some kind of reputation system. But the problem is that it's subjective to something that is called civil attacks. If you actually somehow figure out that that particular peers are mining, you can target your attack to the miners. They are kind of like this weak part of the entire network. So there are a couple of ways to avoid that. Like mining on two nodes in parallel or preventing too many peers from connecting to your mining nodes. It would obviously theoretically be possible to attack the network and actually take it down. It just requires enough resources.