Spirits
Spirits are sentient beings originating from the metaplanes. Under some circumstances, they can cross the gap between their dimension and ours. A lot of magical tradition manage to invoke a specific set of spirits.
* Shamans and Druids invoke Nature Spirits
* Toxic Shamans invoke Toxic Spirits
* Insect Shamans invoke specific Insect Spirits as per totem.
* Hermetic Magicians invoke Elementals
* Wujen invoke Spirits of the Elements and Ancestor Spirits
* Tír na nÓg followers of the Wheel are rumored to invoke the Wild Hunt at a high rank.
Free Spirits
Some spirits, however, don't need the commands of a magic user in order to come into our world. These spirits are called free spirits. They cannot be summoned without their true names and are very powerful.
Bad things that go bump in the night
And then there's the various really nasty stuff, such as the Shedim or the Wraiths, and even worse things lurking beyond the deep metaplanes…