In addition to Krystal's appearance as an Assist Trophy in Super Smash Bros Ultimate, she is featured as a Legend Spirit, the highest ranking of Spirits. Her challenge can appear randomly on the Spirit Board, as it does in the video above. Krystal can also be found in the World of Light mode, towards the end of the map, near Wolf. Check that out in the video below at about 54:16. Lastly, Krystal's Spirit is apparently available for purchase in the Spirit Store for a whopping 15,000 Gold!