If one where to make a Papyrus variant from the gemknight au, what factors are important to keep in mind to make one properly??
You can do what you want forever! However, here are some general rules I like to follow:
-in his late 20s
-soul is a gem (this is true to all monsters in the au)
-a second gem is worn which helps in making magic bullets (also true for all monsters in the au)
-over 7 feet tall/over 210 cm tall
Much like any character, he is shaped by his environment. I like to give them general Papyrus traits,but also keep in mind how their circumstances affect that. A fun one is to put a metaphorical wall between him and others- difficulty communicating his needs. Take Amber for example, talks a lot, is exremely active, but is so good at hiding his baggage that at worst he'd come across as shallow, and he convinces himself of this too, because facing his own needs would be worse. Like somehow this guy never talks about himself in depth but it looks normal to people around him because he's cheerful about it. Or take Sharp, who has difficulty really trusting people around him due to the nature of his world, but oh how badly he wants to trust someone. And he believes that he can, because even if that's a foolish hope, isn't it worse to have no hope at all?
Or in other words, give him some reason to have a metaphorical mask. What is he under that? Does he even know, or does he hide it from himself too, ,because that way the mask will be more convincing?
So I guess my advice is to take Papyrus (the coolest, the original), then give it some thought, how you think he would be shaped by a gemknight environment. (base gk is that monsters are within a dome-like barrier out at sea on some islands, sometimes humans attack, so they have to have some way to defend, and that monster souls are gems)
I hope this was helpful! And if you make a gk papyrus, I would very much like to see! This is absolutely up to you, but I am curious.