So, in the pic of Skinwalker Gloomweaver, there's this green thing curling up beside him. It looks like his pouch is tucked behind it. Do we think that's, like, a cloak or more like a tail? I have no idea.
To me, it looks like he has the book in a sling and the big tail is in addition.
Defintely looks like a snakey tail, I wonder if it has anything to do with his spirit snake thingy
Interesting angle! Never would have thought about that
I had also assumed tail. By the by, did anyone else blush a bit at first Gloomy glance? His pose seemed ever-so-slightly provocative when you aren't thinking about it. Let one buttcheek rest on the tomb, lean back ever so slightly, raise on leg at the knee...I think he's presenting.
We've stumbled upon mating season of the GloomWeaver!
Did you just open the door to rule 34 fanfiction? :P
I'll just point out original flavor Gloomweaver also has the serpent tail: http://sentinelsofthemultiverse.com/sites/default/files/cards/images/GloomWeaver_0.png
By the way, looking at the old gloomy and the back of DW nightmist... what the heck is that little pink gem he's always holding?
My guess is that it's Joe Diamond's soul.
I'll just point out original flavor Gloomweaver also has the serpent tail:
Sonofagun, you're right. I'd always just assumed that wavy green thing behind him on his original card was some bit of the Realm of Discord floating by. Mystery solved.
New mystery: why does Gloomweaver have a tail in the first place? The world may never know.
This was always in the back of my mind with original Gloomy. Joe is very plausible. It could aslo be a little piece of Nightmist herself. Consider that a part of Gloomys dimension was brought into her, their destinies and fates may be tragically intertwined. When its all boiled down, Gloomweaver is in essence the curse inside Nightmist she has to contend with. DW NIghtmists incap side fits in here rather well. She has to confront him face to face, alone, in order to reclaim herself and facedown her greatest challenge.
It could also be Joe. Just saying haha.
The tail might just be there to facilitate the aforementioned fanfic.
I bet he's holding abneverlasting gob stopper. It has laste an eternity so far.
The tail's not showing on Dark Watch Nightmist's flip side. It's a tricksy tail.
Well, I imagine he's sitting on it (or that "chair" has a hole in it to allow the tail to go through behind it). 
DWNM's incap does NOT show Skinwalker Gloomy. We don't know that original Gloomy even has a tail; it might be a side effect of his embodiment in flesh, that his spirit-snake familiar could only come with him by attaching her face to his butt (which is after all where every dark overlord wants his faithful servant to be).
Interesting side-note...the RCIR box shows faces on all four sides, as with the EE box...two of those sides show Fixer and Nightmist, the two heroes who aren't on the top of the box, and a third shows a woman who I presume is the Operative. But the fourth shows someone we've never seen before - a green-scaled snake. I'm assuming this is Ophidia, but we can't see her head on Skinwalker, and she isn't green on her own card, so this is the only place we can see her looking like this. And it happens to be far and away my favorite of the four pictures. Like, if I had a shelf to put SOTM on, I'd rotate the box every time I put it away, to make sure that picture was showing out.
No, I think the snake is Geb.
Oh, duh, forgot about him. Funny they'd show him instead of Atum though (or maybe Set, Osiris, or Isis).
Gloomweaver's normal front side shows him with a tail as well, as was stated earlier in this thread.
Yeah, Atum's the leader, and Set is the most easily identifyably Egyptian. Oh well. Whatevs.