Spriggans are nature-based entities that have control over the environment around them, able to manipulate plantlife. Primal creatures, they're hostile to humans, preferring to burrow deep within the ground and attack anything that would harm their domain... Spriggans that have bonded with humans can be reasoned with however, able to communicate using the human language rather than off of instinct. The Spriggans that grew within a human rather than soil have complex personalities.
They're not fond of depravity, or any kind of decay... it harms the Spriggan and causes physical pain, hindering their growth. The creatures are most content when their surrounding environment is only at the mercy of the four seasons. This isn't to say that they're naturally good creatures--much like the yokai or the animals or the wildlands, they simply have a different mindset to humans.
They're subservient to the deity Asena. The White Wolf has absolute control over nature, and thus the Spirggans by extension.
Ala Eutrice, an alchemist, produced the first seedling in 598AC, using the remains of a strange, extinct creature and refining it through alchemy, which she then let grow beneath the soil. It eventually matured into a Spriggan. What the creature was and the process she used to create new life is a mystery.
A thorned, green seed. The roots set into the soil and a small plant slowly takes shape after a month or so.
A few months in and the seedling can be left in the soil to continue to grow over the years, or it can be harvested and implanted into humans through a specialized ritual. Outside of the soil, a young spriteling has a set of diagonal teeth that snap away. Within a host, a spriteling learns and grows from the experiences of their partner, eventually developing into a Spriggan.
Spriggans are fully matured, and at this stage in their life they can influence and control the domain around them. The size of their domain depends on the strength of the Spriggan. They're able to call insects to act as familiars, and spread their growth throughout their territory. A Spriggan must root itself to the ground, and to kill one, the source of their body has to be destroyed.