Greetings once again fellow Genobros!
As we await the imminent announcement of a Nintendo Direct, I'd like to share an idea in regards to Geno. What if let's say, we got an expansion for the World of Light campaign in Ultimate, consisting of a new map with new spirit battles + spirits to collect, but most importantly with a new threat that must be stopped.
The map leads the player up into the outer reaches of the World (outer space) by means of the giant spiral of spirits that formed after the true ending of WoL. In this new map, an amorphous, powerful being is absorbing the spirits that were released from the World of Light. This new "evil" is a familiar one, but with many faces. At the end of the map, this new "fiend" awaits, bearing its different faces; each of course being a different phase. All of the phases will share three basic parts; a circular core that will glow at its center with a symbol that identifies the current phase, a pair of hands, and a cape. The phases are the following:
Phase 1: Cackletta (Soul)
Core Symbol: Heart
Origin: Mario & Luigi: Superstar Saga
Description: The first phase of this new foe dons the face, claws, and cape of the infamous doppelganger Cackletta from the Bean Kingdom. It will employ attacks such as projecting a copy of itself on the opposite side of the screen, at times both attacking in synchrony. It will also launch fire balls, and lightning bolts at the player(s).
Phase 2: Shadow Queen (True Form)
Core Symbol: Diamond
Origin: Paper Mario: The Thousand Year Door
Description: In this phase, it dons the face, crown, and veil of the Shadow Queen, as well as its shadowy hands. Most of its attacks will consist of it swiping its hands at the player(s) or grabbing them, causing damage. Beware, as its hands will fade out, and reappear when its about to attack. It will also cast a glare that can hit the player wherever they are located on the stage (recommended to dodge since it also inflicts serious shield damage).
Phase 3: Dimentio
Core Symbol: Club
Origin: Super Paper Mario
Description: The demented jester is manifested in the third phase, the core donning its face, neck piece, and hands. It will launch energy projectiles at players, and can create small vacuums that will absorb any who comes into contact with it, and shoot them out with force (careful if at high percent). It can also increase the number of energy projectiles in can shoot simultaneously.
Phase 4: Fawful (Dark Star)
Core Symbol: Star
Origin: Mario & Luigi: Bowser's Inside Story
Description: "I HAVE FURY!!!" Unfortunately this manifestation cannot speak, but its powers are still to be feared. Donning the wily grin and glasses, as well as the claws made of dark star energy. In this phase it will have a smaller dark star orb floating around it, at times approaching the player and firing multiple energy projectiles (alternating between fan patterns, all directions, etc.). The hands will at times try to grab the player(s), which will leave them open to projectile impacts. It will also try to bite the player.
Phase 5: Antasma
Core Symbol: Spade
Origin: Mario & Luigi: Dream Team
Description: The living nightmare is manifested in this phase, donning the fiendish mask, cape, and claws of Antasma. It will attack by transforming its entire body into a swarm of bats, and move quickly to the opposite side of the screen (similar to Dracula's bat swarm attack). It will also at certain moments summon numerous miniature saws that will ascend through the stage (easy to dodge, but if hit by one, it could lead to being comboed into the others). It will also fire projectiles of energy (somewhat larger than those fired by the previous phases), and can also summon orbs of nightmare energy around the player that will circle around them until they draw into each other to hurt the player (dodge when the circle's about to close).
Phase 6 (Final): 
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Core Symbol: None
Origin: Super Mario RPG: Legend of the Seven Stars
Description: The final phase recreates the face, hands, and cape of a dear, yet long forgotten friend. Corrupted by the passage of time and loss of faith, the core reveals its true form, posing the final challenge to the player(s). It's attacks are variations of ones the starling could perform in the past while possessing the Geno doll. It's hands can shoot rapid-fire rounds of bullets, as well as fire larger bills (cannon balls) from its hands' neck. When both hands are raised, reaching almost the top of the screen, it will fire numerous, random beams of light (of different colors) towards the stage. When it moves towards one side of the screen, it will prepare to fire off a powerful beam (a buffed Geno Beam). When it's HP threshold reaches critical levels, it will begin to use a buffed version of Geno Flash. It will move towards the background, and its face will transform, recreating a high-tech cannon that will fire off a sonic blast (it causes low damage, but has absurd knockback; similar to Tabuu's attack which could send player's off the screen in an instant).
After defeating this foe, the core will fall onto the stage. A CG cutscene then plays, showing the core beginning to crack open, as light begins to shine out of it. As the core cracks open, from within it comes out a small, bright star. As it moves around, flying curiously around the fighters, it then flies off, and the spirits are once again released. The spirits carry the fighters back to the surface, as the sky is now a clear blue. Near the end of the cutscene, once all the fighters arrive on the surface (near the hill from the opening of WoL), a mysterious fighter walks towards them. It's Geno, finally making its entrance. The other fighters welcome him; Mario, Bowser, and Peach knowing that he's
♪!?, and are overjoyed to see him back to normal.
