Avril Lavigne

Quoting both of y'all because it worked. THANK YOU.

Edit 3: HOLY FUCKING SHIT. I'm probably the biggest idiot to ever log in to Serenes. I did literally everything but turn the volume up in the actual program. I think I deserve the biggest slap in the face right now.
SOLVED. Fuck me sideways.

Nightmare is not used for inserting. Nightmare is mostly used for changes and not insertions. FEditor is the program that let's you insert custom battle animations, which is what it sounds like you're trying to do. I'm not sure if you know how to script battle animations, but it could be a lengthy learning process. You're going to need to Google some tutorials on that if you don't know.
So no, it's not possible to insert a "custom character" on Nightmare. Plus a "custom character" really only means a custom portrait, unless you want that character to be unique with its own class.
I would explain everything to you if I had time, but there is plenty of tutorials that will help you make your own "custom character" and use it for whatever you like.

FIGURED IT OUT. For some reason had to reinstall it.

That still didn't seem to help. Next time use more detail.
Usually this problem occurs with the promotional item itself. I don't know if you're having trouble with that but I'll tell you anyway. In the Class Editor (Nightmare), it tells you what you want to promote the class to. So when you apply the promotional item of your choosing to that character with that class, it should promote them.
The way you edit which classes the promotional items work on, you have to go to the Item Editor and find the promotional item module (duh). It allows you to point to a custom offset for you. Then there's a module that allows you to edit these offsets to the desired classes that you want promoted with that item.
I don't know if that is what you are looking for but you didn't say too much and it makes it difficult for us to know what you want help with.

So are you using the Misc Map Sprite editor in Nightmare? Because if you are, class 0x61 is actually in the 0x60 slot there. It's weird. Everything is shifted down by 1 in that module (I am using old-school Nightmare, not sure if it's the same with the new), and make sure your Graphics Pointer is different than your Animation Pointer. You can use Animation Pointers from other classes too. I haven't found that it does any harm.
Just see if that works, and if not, then someone more knowledgeable than myself will come to correct my mistakes and help you!

Aahh... okay yes that pattern seems to make sense. Thank you