Whipped up a Rex/Pyra/Mythra team moveset based on XC2's switching mechanic.
Design Concept: Vanguard and Rear Guard. Rex can switch between his blades, and his blades can even take control of the combat using the Aegis Sword. You play as the Vanguard, and are supported by the Rear Guard. By default, the Vanguard is Rex and Pyra is the Rear Guard. When playing as Rex, switch between Pyra and Mythra using Shield + B (like Inkling's Ink refill). Or switch between Vanguard and Rear Guard using Down Special.
Rex:
Neutral Special: Sword Bash - Rex charges ala Little Mac's Straight Lunge before dashing forward sword pointed first.
Side Special: Double Spinning Edge - Rex spins his sword in front of him. Pressing the command again will cause a second swing to be performed without any ending lag after the first.
Up Special: Anchor Shot - A tether recovery using the anchor gun.
Down Special: Vanguard Switch -> Rolling Smash - If Rex becomes the Vanguard, he will perform the attack immediately after switching, which is a dropping sword attack in front of him.
Shield Special: Blade Change - Switch between Pyra and Mythra, who follow you on the battlefield.
Passive: When the Rear Guard, Rex provides a passive buff of increased attack and jump height as long as he is close to the Vanguard. With Rex, damage output is consistent with the sword. The rest of the moveset consists of punches and sword attacks ala Shulk.
Pyra:
Neutral Special: Flame Nova - A quick attack with a small AoE flame ring, wide but not tall.
Side Special: Blazing End - The Aegis sword turns on fire and does two full spins in front of her. Think Palutena's F Tilt, but bigger and more damaging.
Up Special: Prominence Revolt - A flame pillar appears underneath Pyra so she can recover.
Down Special: Vanguard Switch -> Burning Sword - When Pyra becomes the Vanguard, she'll drop a small meteor in front of her.
Passive: When the Rear Guard, Rex provides passive buffs of increased shield damage and reducing damage to your shield. With Pyra, damage output is stronger the closer to the hilt you get (referencing to Pyra not being as adept at fighting when compared to Mythra). She attacks with the sword, punches, kicks, acrobatics, fire balls, fire walls and fire pillars.
Mythra:
Neutral Special: Ray of Punishment - a quick laser-like attack, like Shooting Star Bit
Side Special: Lightning Buster - Similar to Dancing Blade, only one attack pattern is possible. The attack is quicker to make up for it.
Up Special: Photon Edge - Pyra makes a quick dash in a direction, disappears, and reappears with a sword slash.
Down Special: Vanguard Switch -> Sacred Arrow. When Mythra becomes the Vanguard, she'll fire a small barrage of light arrows in front of her.
Passive: As the Rear Guard, Mythra provides a passive speed buff and air speed buff. Her sword is strongest at the tip, and she attacks with the sword, punches, kicks, acrobatics and light arrows.
Final Smash: Siren. The blade calls upon Siren, who appears in the background and fires a barrage of lasers akin to PK Starstorm. The blade also changes form to their spoiler version and Rex puts on his spoiler equipment for the duration of the move.
Rex' costumes are based on himself, Nia, Vandham, Zeke, Tora, the other spoiler party member, Jin and Malos.
Pyra's costumes reference herself, Mythra, Brighid, Poppi, PoppiQT, Disguised Pyra, Pandoria and her secret form.
Mythra's costumes reference herself, Pyra, PoppiQTpi, Chapter 7 spoiler blade, Malos, LKOS-MOS, T-elos and her secret form.