This is a heart shaped tail tip that fits the end of a Costail. For a more in depth written article on how to slice and print this, follow this link:

We have bot included the stl and the Prusa project file if you use this slicer.

Summed up:

Download STL/3mf file from thingiverse
Import STL file into your preferred slicer software. We use Prusa slicer.
Use the following settings:

Nozzle diameter: 0,4 mm
Layer height: 0,15 mm
Vertical Perimeters: 2 outer perimeters
Infill: None
Supports: Custom square support enforcers
Brim: 10 mm
Material: PLA, PET(G) or your preferred filament.

Export the sliced file and print it on your 3d-printer of choice.