While playing the mod, I noticed some mobs are the same as the Overworld ones, whereas others are different (like the boars, big-horned sheep and deer) so I thought it would be a cool idea to make a variant of the wolf; which I've unoriginally named the 'Twilight Wolf'. I understand it probably won't end up being canon, or at least won't be anywhere near a top priority, but I thought I'd suggest it for the fun of it. I'll include some concept art I quickly whipped up if you're interested :)

1. just a basic look at the wolf and some ideas for markings. Unlike the eyes and mouth, I don't think the markings would glow, they're more just natural fur patterns. The legs fade to a darker purple, but I'm not sure if that fade would be solid or maybe translucent like the kind of bubbly shadow bits.
2. cameo from Steve petting the pupper- also used to show that the twilight wolf would be semi translucent, at least ever so slightly, though they could also probably go 'full shadow' when hunting prey like boars or deers, all aside from their eyes/mouth which stay opaque and glowing similar to an enderman's.
3. just a size reference compared to the player
4. when tamed, rather than having a collar, the wolf's markings could be dyed (possibly with special-made 'spirit dye', though that could get more complicated). On the topic of taming, you'd probably only be able to tame the pups. The adults would act the same as regular wolves, ignoring the player unless provoked - though I could also see them being hostile as a default similar to piglins (or maybe only if they're 'tamed' by a certain boss or in a certain area or something)
5. an edit of the saddle icon to make it a 'spirit saddle', which you can equip to a tamed wolf to ride them

I'm really sorry if I'm being too forward with this suggestion, it's my first time doing something like this, but I'd love to see what you think of the idea! Thank you guys for making such an amazing mod