Another idea for a Krystal reveal:
On a landscape of some sort, (or in the Great Fox,) Fox is shown sparring Falco. The two throw playful, but competitive remarks at each other during the sparring. After they're done, it cuts to gameplay of Fox and Falco in an actual match.
In the midst of the dialogue, we hear a familiar voice which chants, "Playtime's over, Star Fox." Wolf jumps into the fight and begins to face both of them. When Wolf realizes he is outnumbered, he calls in his new Final Smash, "Star Wolf." This Final Smash summons a Wolfen strike from the members of Star Wolf. We see the FS used in the game and then we approach a CGI cutscene which shows the fight between the 3 characters and the Wolfen Assault on a new landscape. Soon, 2 Arwings appear from the sky, followed by the Great Fox. It's Krystal and Slippy, who've come to give Fox and Falco aid against the Wolfen. In the midst of the battle, Slippy is being chased by Panther. While Krystal flies to save him, Leon hits Krystal's arwing and causes her to lose control and crash. All of this causes Fox and Falco to be distracted and Wolf attacks both of them in quick succession. As the 2 lie there in pain, Wolf stands over them and smiles, mocking them. Out of no where, a blast strikes Wolf and launches him from the 2 injured fighters. Panther and Leon flee to assist Wolf and from a distance look into the direction from where the blast came from: The wrecked Arwing.
Everyone looks over to the wrecked Arwing and soon, a shadow ejects from the flames. In a graceful landing, the camera pans out to show Krystal holding her staff, with a Gatling gun on her back. She simply flips her hair and says, "That's no way to treat a lady!"
She then flips her staff around and strikes a fighting pose. As she strikes it, the newcomer paint is shown with caption, "Krystal flies into the fight!"
Fox, Falco and Krystal all stand next to each other and jump towards the screen. We then get a showcase of Krystal's moves.
At the end, we see Slippy from the cockpit of his Arwing looking on the 3 of them. He then says to Peppy, "I guess we don't have what it takes, right Old Guy?" Peppy agrees, but Slippy then says, "Wait....I have an idea!!" Then we get a brief showing of Slippy as an Assist Trophy.
Might be extremely flawed in spots, but that's what I came up with
Let me know what you think!!