Design your own Fantastic Beast.
a copy of the book "Fantastic Beasts and Where to Find Them"
paper
pens/pencils/crayons
Use the Fantastic Beasts book as a guide to design your own animal.
Provide supplies to your party guests. Explain that you will be creating your own magical creatures field guide. The guests will design a new magical beast. They can create anything that they can imagine. Once they have drawn their beast, the guests should write a short description of the "animal". Use Fantastic Beasts as an example for them to follow in their descriptions. Make a nice cover and "bind" the pages together to create your field guide.