All skins (Sim head and bodies) come with all the necessary meshes and other files, and should work regardless of which expansion packs you may or may not have. Any exceptions to this rule will be specially marked.

"Fetch" the Skeleton Dog

Based on the little ghost doggy you see in the Pumpkin Hill level of Sonic Adventure 2. Ain't he cute? :P
"Pyro" the Sim

My TS1 "avatar" when I first started playing. Let's see, this character has an Invader Zim T-shirt, black leather jacket... um, wings... Gee, do you get the feeling this character is just a little bit serty...?

I also made a version of the same outfit without the wings.

These are the original adult kelpies available on Simblesse Oblige. They are based on Norwegian Fjord horses and come in two base tones, a slightly warmer brown (female) and cooler grayish (male). These are regular, everyday skins.
Cthulhu (or Cthulhoid)

The Great Old One himself... or perhaps one of his many Star-Spawn, if you prefer. I do hear that they are somewhat less accosting to one's sanity.

Includes everyday as well as formal, pajamas, swimwear and nude skins.
Deep Ones

The followers of Dagon and Hydra, many Deep Ones started out looking like regular humans before gradually metamorphosing into something decidedly less wholesome. By far the coolest of Lovecraft's creations, if I may say so.

Includes three default skins (those pictured) as well as custom pajamas, swimwear and nude skins.

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As featured in The Shadow Out of Time; their appearance is based somewhat on the game Call of Cthulhu: Dark Corners of the Earth. The Yithians were known as the Great Race for they were the only race to ever master travel through time as well as space.

Includes everyday as well as formal, pajamas, swimwear and nude skins.
Spare Hands - The Grim Reaper
The playable Grim Reaper skin available at Bloody Sims is fun and all, but when I started using it in my game I realized it lacked one important detail: some of the hand skins were missing, which meant pink flesh would randomly appear on old Grim's hands when he performed certain actions, put his hands on his hips, etc. These are copies of his normal hand skins, just renamed to provide a full set of defaults. That way he won't suffer "fleshy hand syndrome" any more.
Spare Hands - The Nazgul
The Nazgul skin created by Noxeen at TSR suffers the same problem as the Grim Reaper: sometimes his hands flash pink, which looks really weird. These additional files solve that problem.
Twilight Sims

A collection of characters from the movie Twilight. Why did I make these Sims? I have no idea, I'm not really a fan. There are no bodies included in this set... just heads. Six characters are included: Edward, Emmett, Jasper, Alice, Carlisle and Esme. Yes, that does mean Bella and Rosalie are missing... I couldn't find meshes that suited them so you'll have to find stand-ins somewhere else. That's what happens when you have distinctive-looking hair!
Or maybe you're looking for other vampires? You know, the non-sparkly kind?

Then check out The Lost Boys Sims at The Lost Sims! There you can find David, Marko, Paul and Dwayne and Max, and a few objects, like David's "wine".

And also be sure to check out Biedersims, where you can download the "Elixir of Eternity" which will make Sims real vampires... up to and including the whole biting other Sims thing. Yes, for reals. It's almost like having Nightlife in TS1 (except with the whole burning up in daylight thing). A definite must-have!
I own none of the copyrighted elements mentioned here, including The Lord of the Rings, Sonic the Hedgehog, Invader Zim, Portal, Twilight, etc. etc.
I have no affiliation with Maxis or EA. This content is offered freely as per their terms, no profit is being made whatsoever. Anything made available here which was a collaborative work with another developer is posted with that person's permission.