Ooh, I always adore playing with "light" and "dark" motifs, with interesting results...

Same

Thanks!

What makes the Shadow types different?

I guess I just lack any real naming conventions for the ghosts, so I just call these "Shadows" because, well, they're dark, shadowy entities. While the smaller "child" ghosts tend to have a light, misty or foggy or cloudy appearance, these ones are darker and appear smoky or shadowy, for reasons I have yet to determine--or may forever leave ambiguous, you try capturing one of these in a bottle to study it and tell me how that goes!
One advantage this form offers is the ability to blend seamlessly into the shadows without dematerializing, a useful attribute for hunting and for hiding.

These ones tend to come from adult creatures, and as a result they tend to be more angry, bitter, and aggressive, regardless of what memories they retain from their past lives. That might be because they have an understanding of death and want revenge, or have regrets or unfinished business, as cliche as that may all sound, or were just too angry to truly die.

That doesn't mean they're always hostile, despite their fearsome appearances, though. I have been thinking, based on last year's drawing of one of the Shadows interacting with Puppy Ghost, that there could be some fun story potential there--the Deer Shadow probably isn't too fond of canines, and probably initially resents the presence of the overly active and curious Puppy Ghost cooing and floating in circles around them, but quickly (albeit a bit reluctantly) takes on a protective "babysitter" role toward the newly deceased cub when it becomes clear the little one doesn't quite understand that in this new form it might be harmed by the high voltage running through a street lamp or that it shouldn't wander unwelcomed into homes.
Given that neither ghost would really speak, something like that would have to be conveyed purely visually, like an old cartoon, relying much more on body language and their expressions rather than their words.

There could be some potential there for balancing out the hostile/not hostile angle. It could be that some are acting as protectors for an area, item, etc... Or perhaps trying to actually be protective to the people in an area, because of something being dangerous about a location, object, etc... But as you said they don't really talk, they can't just directly communicate things like: "Stay away! This is a dangerous area!" or "Hey, I need my privacy here!" or "Don't touch that/go in there!", without using a more fearsome approach. This could quite easily lead to people assuming that more of them are hostile than they really are. Combine that with the ones that actually are, and you've got a good reason for people to be wary of these ghosts.

That's definitely an angle I have considered playing on... I think the first time I posted art of these guys a few years back, I mentioned how they tend to be protective and territorial at times. Part of that may be basic animal instinct, sure, but I do like the idea of them also acting in the interest of their living counterparts and trying to scare them away from dangerous areas. That might explain why some ghosts linger in the places where they died, to warn others in hopes of sparing them a similar fate. Or, like when I was describing my ideas for Deer Shadow and Puppy Ghost, the more fearsome ones might serve as protectors of the more playful and innocent ones, ensuring the young ghosts can find some peace in death at least... or at the very least, avoid getting caught in a jar or something. I'm not sure what, if any, ghost containment and repellent technology might exist in-universe yet, but it probably involves electromagnetic fields and blinking lights.

I suppose the more malicious ones may hunt in packs, though, and play on the exact opposite--generating curiosity. If you wanted to feed off the life force of the living, I can't think of a much better approach than to lure would-be "paranormal investigators" into some remote, dilapidated building in the dead of night!
I suppose such an approach would lose a bit of efficacy in a world where ghosts are a natural but not-well-understood aspect of nature, though...

Curiosity is a very strong force, in any universe. It might be a bit less Ghost Hunters and more properly set up scientific study attempts, but so long as they aren't fully understood, there's going to be someone out there trying to understand them.

This makes me think of studying sharks--sure, we understand that we're trying to study them, but do they understand? Or do they just see a potential meal swimming by?

I do need to give this overall concept a bit more thought, as it's entirely possible to interact with and communicate with these ghosts and I'm sure that there's at least a few that aren't angry and territorial and reclusive. I have some physical limiting factors in place, combine that with centuries of folklore and urban legend and rumor, science perhaps not developing along quite the same lines on their world as it has on Earth, and perhaps some sort of instinctual aspect to both the living and the ghosts that makes them tend to want to avoid each other and that would probably pretty easily explain why they're not well understood. I guess it would be like if there was any serious scientific study attempts directed at Bigfoot, but Bigfoot didn't want to be studied, and we'd be left with a lot of blurry photos and damaged study equipment but at least have some scant but solid evidence to confirm their existence.

I totally have an authentic picture of Bigfoot in a river, from the 80s. You can see the driver and everything. ;P

So that's why the cameras are always smashed up after a Bigfoot encounter, they've been run over...

All those Bigfoot hunters need to stop making fools of themselves out in the woods and just buy themselves some monster truck rally tickets. Then they can observe Bigfoot in its natural habitat.

Reminds me of Shadow Mario

I'm not familiar with Shadow Mario, so I can't really comment on that, sorry...