I'm imagining skeletal animals for the most part, created by humans for a specific purpose, like a skeletal horse used to pull a wagon, a skeletal guard dog, a skeletal cat used as a mouser, etc. The main benefit of them being not alive is that they wouldn't need food, water, rest, etc. Pure magic seems to be the easiest route to go but it also seems a bit boring... thoughts?
I'm sure there is another way to do it, but pure magic seems to be the easiest. I also like Brindy's suggestion. The trick is simplicity, right? To suspend disbelief in your reader in a way that doesn't require copious explanation. If I were doing this, I would spend my time thinking of a way to do it that can be simply explained in a sentence.
Mechanical bits were my first thought too. Mmm robots. Really it depends on your setting. What level of technology do you want / what kind of magic do you want? How can they interact? Maybe the bones are held together with brass brackets and hinges and given locomotion through magic. Though that does make me think why not just straight up metal automatons, because while you might not have to feed a skeletal dog, it will get fairly brittle unless your magic keeps the bones nice and dense. But that's irrelevant if you don't have sufficiently advanced tech. I also don't think that pure magic has to be boring. Just make it interesting magic. Maybe sacrifices have to be made in order to power your skeletons so it adds depth to the setting; maybe you etch spells into the bones so it's visually distinct. Nothing wrong with just magic.
To hell with easy. You would have to be a necromancer to reanimate the bones and infuse and bind them with just enough soul essence to make them obedient but not too smart. You would also need to apply some elemental magic to strengthen and reinforce the bones so that they don't come apart too easily, or else find a mage or wizard who can do it for you.
Your post reminded me of a creepy YouTube video I watched a few weeks ago where Russian scientists in 1940 reanimated a dead dog's head. Very freaky video. (if you go looking for it, look up Russian scientists successfully reanimate dead dog's head Anyway, instead of magic you can think along the lines of scientific discovery that is so advanced that they can reanimate things, like maybe there's a wire that keeps all the bones together and a computer chip is located somewhere on the structure to make the bones move.
Skeletons by themselves are incapable of locomotion. If an external force could animate a skeleton, then that force could just as easily animate rocks, wood, etc. for the same purpose. It'd be more plausible to re-animate dead muscle tissue.
If you want to go the technological route, then I can easily imagine some form of semi-exoskeleton (no pun intended) holding the bones together, with tons of wites, cogs and stuff and a simple computer making it all work. But that may just be my Warhammer 40k fanboyism speaking. Speaking of which, they do have something like in the setting called "servo skulls". Skulls of dead servants who wanted to serve the emperor beyond death, so their skulls get "reanimated" through technology. An example: https://s-media-cache-ak0.pinimg.com/736x/0d/e7/4b/0de74bc344b4ab54cadc9f2bd7f651e3.jpg I've always been interested in the idea of ghouls, zombies etc made through technology and robotics instead of magic.
