Zerrsyntho is by @Emerald_Hopper, therefor he has the right to say whether his creation is a rayurien or not. Not you. Since he's saying Zerrsyntho isn't a rayurien, then you can't make it one. Plus, I made the rayuriens, so I could make Zerrsyntho a rayurien, but I'm not. I'm going to respect Emerald's wishes because I'm a good person who understands copyright.
