By the way, regarding getting rid of the "extra" creatures, I eliminated all creatures except for one imp, but they still won't let me pass through the portal a second time. And if artifacts are interfering, you still can't get rid of them – you can't give them to anyone because there are enemies everywhere, and you can't sacrifice them either – it's an evil race, and the altar requires creatures.

P.S. Here are a couple more battles with neutral creatures that I enjoyed: