[@AtomicNut]: Like I said over PM, demons are a bit more complicated then that. ^^;

For one thing, yes you can totally summon them, but they're mostly in the world already. They're not really fond of Hell(given Hell is a warped, twisting hole in reality caused by Lucifer[the archangel's] fall). It's not a very fun place to be.

They're also all former humans who became demons due to Lucifer's fall around 1000 years ago. Well, the originals are, the child of a demon is always a demon, they just have very low birth rates.

They look human but in some cases have features like wings, tails, horns, or even some animal features.

There's totally spells to summon them(fairly involved ones given you need to set up a whole room for it), but they don't possess people unless it's an actual ability they have.

That being said, there's malignant spirits and stuff. It just wouldn't be an actual demon.