Checking through Spriters-Resource, Wreckingcanon found a custom Krystal sprite for the unused Star Fox 2 Battle Mode Selection Screen. This was made by Arima, and it was posted back in July 2017. You can view and download it on its Spritesheet Page.
Speaking of sprites, don't forget about all the Krystal-related sprites by SmithyGCN:
- Custom Krystal Spritesheet
- Krystal Spritesheet
- Krystal Sprite Animation
- Special Effects
- Krystal Profile Sprite
Thanks to Wreckingcanon for the heads up.