Note: I'm only doing this for a few characters. If you see characters that aren't featured, it's because I couldn't think of anything for that character.
Mewtwo
Neutral 1, Aura Sphere; unlike Lucario’s, goes MUCH faster upon full charge and can’t be stored
Neutral 2, Psyshock; Mewtwo forms psychic blobs that shoot out in a cone-like shape, and cannot be used mid-charge
Side 1, Psycho Cut; Mewtwo sends out two psychic blades in front of itself, but only one when B isn’t held
Side 2, Me First; Mewtwo steals the closest opponent’s held item from far away
Up 1, Power Swap; Mewtwo switches places with the opponent, meteor smashing any opponents swapped to its original position
Up 2, Guard Swap; Mewtwo switches places with an opponents, and is enveloped in a barrier that negates damage until it reaches the ground
Down 1, Future Sight; Mewtwo automatically counters an attack it sees in the future, ranging from 2 to 5 attacks in advance.
Down 2, Miracle Eye; Mewtwo is temporarily able to ignore transformation effects that alter damage.
Young Link
Neutral 1, Light Arrows; a fully charged shot briefly paralyzes the opponent
Neutral 2, Ice Arrows; a fully charged shot freezes the opponent
Side 1, Double Cutters; fires two fins that go up and down respectively, and then the opposite directions upon returning
Side 2, Ripping Boomerang; one of Link’s customs from Smash 4
Up 1, Super Spin Attack; Young Link surrounds his sword in magic that deals more damage, but goes up less vertically
Up 2, Whirling Leap; one of Link’s customs from Smash 4
Down 1, Deku Bomb; stuns opponents in a big area
Down 2, Bomb Flower; travels farther and has less weight, but goes off quicker
Lucas
Neutral 1, PK Flash; Ness’s Neutral B, but with the movement of PK Freeze
Neutral 2, Free PK Freeze; Lucas can move PK Freeze anywhere, but it can’t freeze opponents unless they’re at higher damage
Side 1, PK Fire Wall; Ness’s Side B, but it only appears straight in front of Lucas
Side 2, PK Burst; Lucas tosses a small flame a short distance, exploding with a bomb’s radius
Up 1, Circle PK Thunder; Lucas moves a ball of thunder around himself
Up 2, Rolling PK Thunder; one of Ness’s customs from Smash 4
Down 1, PSI Barrier; Lucas summons a barrier that nullifies all attacks, but breaks after 6 seconds
Down 2, PSI Vacuum; one of Ness’s customs from Smash 4
Roy
Neutral 1, Shield Smasher; Marth’s Neutral B from Melee
Neutral 2, Flare Tempest; Roy summons a circle of flames around him
Side 1, Effortless Blade; one of Marth’s and Lucina’s customs from Smash 4
Side 2, Double Lion; Roy performs two swings that move him forward; based on one of Alm’s Combat Arts from Shadows of Valentia
Up 1, Dim Blade; Roy goes up much higher, but deals less damage
Up 2, Deicide; Roy rises up high, then crashes down and unleashes a fiery shockwave; based on the finishing attack Alm performs on Duma in Gaiden and Shadows of Valentia
Down 1, Push Counter; Roy flings away any opponents who attack
Down 2, Distant Counter; Roy counters with a crescent-shaped flame projectile
Cloud
Neutral 1, Super Beam; Hits multiple opponents and travels slower
Neutral 2, Frail Beam; Travels fast, but deals less damage
Side 1, Octaslash; Cloud slashes eight times
Side 2, Renzokuken; Cloud slashes four times with timed button presses
Up 1, Meteorain; Cloud jumps and slashes down for an instant meteor Smash
Up 2, Rough Divide; Cloud jumps up once and deals multiple hits with his slash
Down 1, Riskcharge; Cloud slowly takes damage while charging his Limit Gauge, which pays off with a Finishing Touch that can possibly instantly K.O.
Down 2, Quick Charge; Cloud charges his Limit Gauge in 5 seconds, and uses a multi-hit Finishing Touch with pathetic knockback
Corrin
Neutral 1, Dragon Fang Bolt; Quickly charges an electric shot that deals multiple hits
Neutral 2, Dragon Fang Flare; Slowly charges a flare that explodes in a huge radius and deals immense knockback
Side 1, Deathly Lunge; Can instantly K.O. an opponent at high damage if timed right
Side 2, Evasive Lunge; Bounces Corrin backwards
Up 1, Dragon Soar; Soars very high but deals no damage
Up 2, Dragon Burst; Jumps at a pathetic height but explodes in a small area upon contact
Down 1, Counter Stomp; Stomps the opponent directly in front of Corrin
Down 2, Burst Surge; Stomps the ground after a bit of charging
Inkling
Neutral 1, Splattershot Jr.; a weaker Splattershot that uses no ink, but also can’t ink an opponent
Neutral 2, Splattershot Pro; fires farther, but goes slower
Side 1, Carbon Roller; turns are easier, but opponents can’t be buried
Side 2, Dynamo Roller; moves slower, but can fling ink while turning
Up 1, Fixed Super Jump; Inkling jumps in an arc, splatting on the ground and can’t change directions midair
Up 2, Quick Super Jump; takes less start-up, but deals no damage and doesn’t go as high
Down 1, Suction Bomb; can be attached to any surface
Down 2, Toxic Mist; Inkling throws a glass bomb that explodes into a poison
Ridley
Neutral 1, Rapid Breath; Ridley can shoot multiple fire balls without charging, but they get weaker over time
Neutral 2, Mega Fire Ball; Ridley shoots one powerful fire ball that takes longer to charge
Side 1, Space Pirate Toss; Ridley’s grab travels farther, but only tosses the opponent rather than crushing them on the ground
Side 2, Relentless Rush; Ridley’s grab doesn’t travel as far, but he has super armor and the grabbed opponent can’t escape
Up 1, Safe Blitz; Ridley travels much higher, but can only go straight up and deals no damage
Up 2, Fire Blitz; Ridley jumps up two times, then flies straight up with his wings on fire
Down 1, Skewer Rush; Ridley charges up, and then flurries the opponent with multiple stabs
Down 2, Skewer Kill; Ridley charges up a powerful skewer that instantly KO’s opponents at high damage
Simon/Richter
Neutral 1, High Axe; travels higher, but covers less horizontal distance
Neutral 2, Hand Axe; travels further horizontally, but only JUST stays above the ground
Side 1, Oak Stake; a weaker variant that falls on the ground and doesn’t return
Side 2, Throwing Star; throws a shuriken that deals multiple rapid hits but doesn’t return
Up 1, Heavenly Uppercut; travels MUCH higher, but only hits once and deals less damage
Up 2, Horizontal Uppercut; travels more of a horizontal distance and is MUCH more powerful, but only hits once
Down 1, Holy Line; the flames from the water work how they do in Rondo of Blood
Down 2, Holy Flame; the holy water explodes into a single flame, similar to how it worked in Castlevania 1
King K. Rool
Neutral 1, Spiked Blunderbuss; King K. Rool fires a spike ball that can't be sucked back in
Neutral 2, Blunderpuss Sputter; the Blunderbuss sputters a bit before shooting a powerful shot
Side 1, Crown Toss; King K. Rool tosses his crown onto the ground
Side 2, Crocorang; King K. Rool jumps towards his crown after tossing it
Up 1, Shocking Propellerpack; King K. Rool emits electiricty from his Propellerpack, but travels less of a height
Up 2, Low Propellerpack; King K. Rool travels very low, focusing instead on horizontal distance
Down 1, Gut Wrench; attacking King K. Rool causes him to burp, poisoning the opponent
Down 2, Gut Cleanse; attacking King K. Rool causes him to bite the opponent twice, healing him a little
Isabelle
Neutral 1, Pickpocket; Isabelle gets rid of the item/projectile thrown at her
Neutral 2, Pocket Plus; one of Villager's customs from Smash 4
Side 1, Live Bait; Isabelle catches an opponent right in front of her, and throws them a long distance
Side 2, Electric Rod; Isabelle holds up an electric rod, which shocks any opponents in range
Up 1, Extreme Balloon Trip; one of Villager's customs from Smash 4
Up 2, Balloon High Jump; one of Villager's customs from Smash 4
Down 1, Dud Trap; Lloid jumps up once, then falls down and explodes
Down 2, Lloid Mine; Lloid explodes upon contact or when inputted again
Incineroar
Neutral 1, Hottest Lariat; Incineroar spins around in flames, hitting once but moving a better distance
Neutral 2, Tornado Lariat; Incineroar spins around rapidly, but can't move
Side 1, Take Down; Incineroar charges forward and tackles the opponent, taking slight damage
Side 2, Judo Throw; Incineroar stays in one place while throwing the opponent behind itself
Up 1, Throat Chop; Incineroar jumps up high, then comes down and unleashes a shockwave that paralyzes opponents
Up 2, Dual Chop; Incineroar jumps up high, comes down a short distance, then jumps up again and chops the air
Down 1, Reversal; Bursts in flames, which deals more damage the higher Incineroar's %
Down 2, Swagger; Incineroar flashes a light that stuns opponents in an area