Amulet of blood polymorph

A bronze and copper amulet, similar in look to an old locket. 

When a drop of fresh blood from an beast is placed inside the amulet,  you can cast the polymorph spell on yourself.

The new form can be any beast whose challenge rating is equal to or less than your level

You can only have one animal selected, if you want to change the animal form,  you will have to clean out the amulet and replace it with fresh animal blood during a short or long rest.