A feathered tail for Dummy 13. Created for a parrot kenku (D&D), but could work with other bird-like Dummies. Snaps onto the stand adapter, either the original or modified one. Reaches to around the knee on a normally-configured frame. 

Print with less infill or just one wall if you want to cut down on weight—it hardly affects its strength/ability to hold a pose. Tested at 100% and 150%. PETG recommended but not necessary (PLA will just loosen faster).

Edit: added 100% tail model for clarity/consistency.