By nature, Arvastairans can all formshift. The average amount of forms one has is three (terrestrial, aerial, and aquatic forms) but it is not a rarity to have a few more or less. Usually when one formshifts, they become a much larger version of the animal whose form they take, but they can appear smaller if they wish as well. This does not apply to creatures which are large by default. Depending on how much keirsi they may be manipulating while in this state, they can start to deviate from the standard appearance of an animal as well. The form of magical, exotic creatures, as governed by Onnvuset, are not typically acttainable by most of the population.
Formshifting is, in essence, the compression of your keirsi to a different frequency. Each living being's nantak, their magical composition, is attuned to different frequencies of keirsi. When an Arvastairan is born, they are naturally aligned with a specific frequency. Even with great practise, it is quite difficult to attain more forms, even for fenvasi. However, it has been observed that young children more easily acquire forms than their adults.
Most children experience their first shift around the age of four. It may be a partial, incomplete shift, where they gain some temporary animalistic features but do not actually change their entire form. If a child does not experience a shift by the age of six, it's usually a cause for concern. Despite being fenva, their capability to formshift does not mean they always develop it properly.
Formshifting is mostly utilised for movement. One's movement speed is typically the main trait enhanced while under the effects of a formshift, a trade off for being unable to use your limbs in a fenva manner. It is possible to cast spells and utilise sorcery while shifted. However, fenvasi do not have access to their rosvom during a shift, so their offensive capability is greatly decreased. Another common enhancement under the effects of a formshift is sturdiness. In exchange for less movement, they become much more bulky and able to withstand greater blows.
The formshift you engage in will suffer its own wounds as one's body would. Cuts, bruises, breaks will only persist during that form. When injured too heavily in a different form, you will be shocked out of your formshift back to your natural form. The formshift you previously had wiill sustain the physical wounds, but the exhaustion and pain from being shocked out of a formshift can be incapacitating to some. If the force used against your formshift was lethal, the shock from unshifting could very well be lethal too.
Since formshifting is only possible through the compression of one's keirsi, there comes the question of where everything else besides the self goes.
Application of an abundant mineral called asenhanti is the answer. asenhanti, light purple in nature, comes in the form of a powdery stone that can be ground down to even finer powder. This powder can be mixed into dye, varnish, polish, woven in between threads, or any number of dozens of application methods.
Eventually, it is sealed with an enchantment called asenhantinmei. Once enchanted, the asenhanti will now collapse the keirsi makeup of any clothing materials enchanted with it when it detects the signature compression of keirsi that indicates a formshift.
Collapsed and dispersed, this loose keirsi will orbit the form of the shifter until the compression is released and the enchantment draws the keirsi back into the form of their respective clothing.
Rosvoms are slightly different in that they naturally undergo the process of asenhantileit during creation without having to be specifically enchanted.
Draconic form, which is only found in deities themselves and the children of deities from the Elder generation or prior, is incredibly dangerous. It's in this form that one's keirsi is loosest; without the essence of a powerful god to hold the keirsi together, most souls are unable to allow their orbiting keirsi to drift that far, as that would endanger the individual themselves. When in draconic form, one's conductivity for keirsi spikes, allowing the shifter to condense the power behind their sorceries beyond all natural limits.
Deities do not typically engage in draconic forms, as deities' draconic forms radiate enormous amounts of raw keirsi and will annihilate most things nearby. Rather, they purposefully stay away from it to keep the deadly potential of them far away from the world they crafted. It is also more practical to stay out of it, as shifting into draconic form, even if it is one's natural state in the case of the arva, is incredibly taxing. In fact, though an arva is strongest in its draconic form, it is also at its most vulnerable immediately after leaving draconic form.
Fenvasi with draconic forms are not as catastrophically dangerous. They will not annihilate onlookers and the surrounding environment instantly. Draconic form would be their strongest state, but unlike the arva, most fenvasi struggle to maintain this form for long. It is an exhausting process and as such, is rarely deployed beyond being a last resort for survival. Unlike with regular forms, a young fenvasi will rarely perform a draconic shift while growing up. Some fenvasi with this form do not discover their ability until well into adulthood, while others die never knowing it existed. Draconic shift can be learned at any age, as long as one is capable of performing it, and the training process to maintain a full shift for even a few seconds can take years.