Skepticism, that was expected. It would take time to adjust to such an idea, especially if he came from a place where such things didn't exist. River hadn't had a difficult time situating herself here. To her, it was just like landing on a new planet for a new adventure. The thing she'd had a hard time with was the being alive bit. That had been jarring, but it was to be expected. Finding herself in the middle of a war wasn't that strange either, she was used to trouble. Though on a far smaller scale than this. But River had learned to be prepared for anything, that's what traveling with the Doctor had taught her.
What she was very grateful for in this place was putting her on a linear timeline with the Doctor. They weren't going in opposite directions anymore, and she rather liked it. It was very strange, but she did like it. And she rather liked meeting the Ninth Doctor and getting to know him along with other companions she had not met. So this world really wasn't so bad if one managed to ignore the Apocalypse thing.
"Lucifer is a demon, the one who is behind the Apocalypse. He wishes to kill all of us. To make sure he stays in his cage, we have to make certain the remaining unbroken Seals, if there are any, stay unbroken. I do not know what exactly the status of that is, but we are all still here and alive, so that is a sign the world hasn't ended yet?" She flashed a bit of a smile, though the joke was perhaps an ill-timed one. "Though the threat of Lucifer and his demon army isn't the only danger. Native to this world are things such as vampire, shapeshifters, vampires and so forth. Just as the Seal pulled you and me here, it can also bring threats from other places here. And without warning we can be thrown years into the future here and experience one potential future. I did that recently. Not a pleasant experience. I'd rather not repeat it."