Start with a clear, dry base coat. Apply white polish across the whole nail on each nail. This will be the background your niffler will stand out against.
Once dry, carefully blob your black polish onto the nail you've chosen to put your niffler on in a general niffler-y shape. I went for the ring finger. Use an image of a niffler for reference, if need be. I made mine standing up and holding a gold coin, but you might choose any pose you like. Let dry completely.
While waiting for the black niffler body to dry, you can add some gold details to your other nails. I found gold coins to be the easiest. All you need to do is carefully dot your gold polish around near the tips of your nails, using the brush it comes with, making it look like piles of gold coins are resting there. I also positioned one near my niffler, where I wanted him to be holding one in his paws.
Once the body is totally dry, you are ready to add his paws and bill. Carefully daub on your peachy colored polish, again using a photo for reference. I simply used the brush my polish came with, but if you'd like more detail or control, try using a small nail brush. Let those bits dry.
All that's left is to add the eyes and nostrils. A niffler's eyes are quite beady, so opt for a small tool such as a stylus or toothpick to apply black polish in the appropriate locations.
Allow your new nails to dry thoroughly before applying a clear top coat to smooth and protect your design. As always, I find it best to load up my brush with top coat and daub it onto the design first, before dragging the brush across to cover the whole nail. This helps to reduce the chance of your design bleeding onto another color.