Transformation spells are considered pure fiction / fantasy. Even if they were possible the legand goes: A shaman who transformed into a bear far too often found that one time he could not transform back. He was a bear in form for many days and grew hungry. The hungrier he got the more bear like his mentality became until one day he came upon some food and killed and devoured a great portion of it. It cleared his mind of bear thoughts and he was able to finally transform back to human only to discover he had killed and eaten his own son. The Great Spirits were so angry with him in his foolishness they punished him by making him a bear permanately. He was about to go off on his new life as a bear when the tribes hunters set upon him and killed and ate him thinking he was only a vicious bear. The moral Great Spirits then decided noone may transform into anything again to prevent future such tradgedies. The End
Note: That may be slightly off from the original but the point is It is not possible now if it ever was to begin with.