First, sorry for possible spoilers. I'm not giving any major information, but I'm just saying. Idk the spoiler rules really... So... Be warned... 

[@hatakekuro] I just can't see many ways for it to be used in which it isn't unfair or OP. How would you even learn such an ancient magic. The last person who knew it (Assumed) was Minerva, and I'm sure she wouldn't spill it, or leave a book or scroll around for someone else to pick up the magic. It's not in her character.