I spotted when going through the code that there is the idea that Nuaos will look "angrier" as he stores damage before releasing it but through testing, it seems like he doesn't actually change textures

Also, hi! I'm the person on Curseforge who asked about making a Fabric port of this mod and I'm 95% done with making a port! If there is anything you'd like to chat to me about, feel free to add me on Discord (ZestyBlaze#4208)

Yeah I noticed that as well, I was looking into it. The method I was using for changed textures works perfectly for the Voldon Familiars, so I'm unsure why Nuaos isn't - I'll do some more debugging when I have some free time though!
If you have any suggestions feel free to let me know.

Fixed in the 1.19 version (in dev).