I'm fairly sure it's a - just because the number cant be represented or that its simply too high to display. Basically his mind cany comprehend the number so it doesnt show anything. It's also possible the number is so long that it shrunk it and compressed it together so much that all he can see is a line

Also the old man's soul could easily be in the pendant. Maybe it's the reason the pendant is sentient. I'm more curious who the old man was. My first thought was the ancient emperor since he had space, undead, and the chaos element which seem essential

Why would you assume there is still 2 Mo Fans? I like that no one seems to have questions about his mother. Anyone ever consider that someone knew his talent after he was born and moved him to the science plane for protection and the old man was just responsible for sending him back. They never mention grandparents or anything either so it could of been his grandpa and the pendant really is some sort of inheritance. It could also have merged the souls of both Mo Fan.

Dean Song He should for sure know who he is. Zhan Kong blamed him immediately when that general was hunting him down. Not to mention he watched the fights between the colleges

You gotta consider that the his demon element is too weak and therefore feeds off the power of the other elements. Not to mention he activated the demon element when all his other elements were used up so it's pretty reasonable that they degraded. I imagine as the element gets stronger and if his elemental stars are full he can activate the demon element with little to no side effects for limited bursts.