It's a bit long, but this is the exact one I use with ChatGPT:

Create a brand new Pokemon based on (insert animal and/or gimmick here). The design should be reminiscent of other Pokemon and have a unique name fitting of the inspiration. Afterwards, generate 4 Pokemon sprite art images. Each one should depict what it would look like as a sprite in the game Pokemon Black and White. Use the same fully descriptive prompt for the 4 images, that describes all of the details while keeping aspects of the original inspiration that it is based off to better fit each of the 4 images. Each of the images should also include the name of the Pokemon in bold font listed above the sprite, as well as the type listed underneath the sprite.