The Laidly Worm of Spindleston Heugh -we have a princess turned into a dragon
- another illegal use of Polymorph Spell the Laily Worm and Machrel of the Sea - Evil Stepmother turned him into a worm
The tale of Jorinde and Joringel - poor Jorinde turned into a nightingale and put in a cage by an evil olde witch.
Then there is the Nordic Legend of Skuld's Mother who went from being a hag to a beautiful DarkElven Princess to seduce our hero Helgi.
It is said in battle that Skuld could bring her dead warriors back to life.
Poor Sir Gwain forced to marry the Loathly Lady. She had tricked King Arthur to giver her what she most wanted in return she would answer his riddle that none else could answer.
Back to polymorph - mostly misused as Polymorph Self 1000's of tales of witches changing shape to commit thefts. The most common is for the the Witch to turn into a hare. In this shape they would go into the barn and suck the life out of the farm animals.
For some that was not enough. They would hop right up to a child and jump into the child's arms. To be carried into the house. Then they would suck the life out of all who lived there.
I hope this gives you some idea of how to use Witches in your game and make it up to Folktale Standards.
Have fun and stay away from hares.