Lucky us! During a demo of Super Smash Bros Ultimate (at 3h 28m 44s), we got to see Krystal appear as an assist trophy. She appears, runs around the stage, uses the ice blast, physically beats characters with her staff, and uses an electric attack from her staff. Then, to leave, she spins around and proclaims "You're not ready yet." That phrase is her taunt from Star Fox Assault.
Additionally, we get to see the full Fox McCloud Final Smash in the same match. It's epic!