This board is for any questions you may need answered. Please make sure to read the rules first, just so you don't end up asking something that's plainly stated. =3
Stoffie hasn't updated it in a while. That's the explanation for them not being there.
About Nyghtmares, it talks about them being mountable on their description on the site. It says something about when you build enough trust they will materialize and serve as a mount. Not being Baal, Stoffie, or a magical mod, I don't know what that level of Loyalty is, so you're better off waiting for one of those people to answer that.
Frightmares...... I honestly don't know.
I tried to answer your questions as much as I could, but you're better off waiting for someone else as well to fully answer them. ^^;
Just returned and getting back in the swing of things! 8D; Expect this space to be filled by something interesting soon. o3o; Though I kinda picked a bad time to come back, 'cause I'm still really busy, but oh well. x3; In the meantime, would you mind clicking them? x3;
I'm sorry, I've been swamped with work and final exams are starting for me (like...this Saturday), so I haven't been able to get to the mountable list. It will eventually get a revamp and will have explanations for creatures that are not mountable explaining why.
However, to answer you question, I previously asked Baal and the Frightmare is indeed mountable. The Nyghtmare is also mountable but its relationship with you must be much more advanced. I believe Baal recommended a level of at least 5 for the Nyghtmare before attempting to mount it. I hope that helps :3