This magic involves the caster taking on the attributes of other creatures, typically animals or plants. However, a sufficiently powerful magic user could harness the powers of demons or even the gods. Most never reach this level and remain relatively weak, limited to lower beings. If a sorcerer were to fuse with a creature above their skill level, the results could end in madness or permanent, grotesque fusion. Users of this skill are called Sonem.
The main limitation is mental strength. In order to make the magic work without losing oneself, the caster must be mentally stronger than whatever they are trying to fuse with. If this is not the case, then anything from permanent physical deformities or complete loss of mental stability can occur
As of yet, no one has been able to fuse with a god simply because a deity's mental strength and power are so much greater than what a human could hope to achieve
Alleviating thsese limitations mostly comes through learning. As one's mental strength grows, the caster begins experimenting with more complex life forms. Almost every person who uses fusion has some sort of physical change (unnatural hair color, strange eyes, or partially discolored skin are the most common) that show their failures.