I sure hope Krystal returns in a new Star Fox game and/or as a playable character for Smash. She'd be an amazing fighter to play, using her Staff and giving you the ability to change her outfits.
(Krystal's Assist Trophy form in Smash Ultimate was the only thing I didn't like about her SSB appearance. It's like an insult to me otherwise. Nintendo were just SO close to making her playable.
)