Concept:
Geno in SMRPG is a glass cannon. He's fast, hits hard, and has insanely strong special moves. Geno in Smash will be much the same- very fast, has overwhelming stage control with various moves that cover a lot of space, and special moves that are very strong, but with a terrible disadvantage state that's hard to get out of, and a light weight that makes him easy to KO.
Stats:
Lightweight, a bit heavier than Mewtwo. Above average run speed, quick initial dash with a good foxtrot. One double jump, above average air acceleration and max speed, low-ish fall speed. Overall, above-average horizontal movement, but a bit floaty. Great in advantage, bad in disadvantage.
Timed Hits:
Certain moves will deal double damage if they're executed properly. If timing is slightly off, the move will still deal extra damage, but not the full amount. If timed perfectly, a special sound effect will play, as well as making Geno's eyes sparkle in his portrait. Exactly how timing works is different per-move this gimmick affects. (See Smash Attacks, Grab, and Specials)
Rocket Punches:
For some moves, Geno will attack by firing his hand off his body to punch far-away enemies. In SMRPG, because it was turn-based, the return trip wasn't a factor, but losing an hand temporarily will matter a lot in a real-time fighting game like Smash. For moves where Geno uses a rocket punch, he will actually lose hands, making it impossible to use certain moves until the hand returns.
Moves which only fire 1 rocket punch can be used even if one hand is gone, but using the "wrong" hand will slightly increase the move's start-up time. The default hand for one-handed rocket punches will be noted with each move. Moves that fire 2 rocket punches can still be used with one hand missing, but will obviously have no projectile on one side. The start-up time is unchanged. If no hand can be fired as a projectile, and Geno will make a disappointed facial expression. All the moves have (weak) hitboxes on his arm, regardless of whether a projectile is fired or not.
Rocket Punches act as projectiles. They travel from Geno's body straight forward until reaching a certain distance, before heading back to him with a strong homing. Geno moving won't affect the punches' trajectory. They have no hitbox on the way back. If reflected (only reflectable on the way out) they will immediately travel back to Geno, faster than usual, and hurt him before re-attaching. Unlike most reflected projectiles, his hands deal set damage and knockback to Geno no matter how they were reflected. (Mostly because of how many projectiles he has, reflectors would otherwise be broken against him.)
Normals:
Jab- A quick punch, followed by an arm flex to reveal his Hand Cannon, and a rapid jab bullet barrage similar to Inkling's multijab. Fires a large star from his arm as the finisher. If he doesn't have his left hand, he can only do the first hit with less range, but unchanged damage.
F-Tilt- A slightly slower punch based on his unarmed attack. Pressing A again fires his hand out as a Rocket Punch. Only can use his right hand. Both hits of this attack are useful, unlike similar f-tilts.
D-Tilt- Geno fires a single star at the ground in front of him, with a long-lasting hitbox. Good combo starter, good for 2-framing. Unnaffected by lack of hands.
U-Tilt- Geno raises his hands up in a "praise the sun"-esque pose, a star appearing above his head that hits multiple times. Mostly an anti-air, but can hit very close-by grounded opponents.
N-Air- Geno faces the camera and fires a rocket punch to each side of him, using both hands.
F-Air- A rocket punch directly forward, with a very strong hitbox right as the fist fires that gets weaker when the fist starts travelling. Defaults to right hand.
B-Air- Geno fires three star bullets behind him. They don't travel very far, but are very powerful. Gives him a bit of momentum when used. Similar to Gunner F-Air, in the opposite direction. Unnaffected by lack of hands.
U-Air- A rocket punch sent directly upward, defaulting to his right hand.
D-Air- A downward rocket punch, similar to Megaman's, defaults to his right hand.
Dash Attack- An quick elbow forward, removing all momentum if it hits an opponent. Similar to the toy Geno's "attack" on toy Bowser, but with a bit of an animation to be less stiff.
Smash Attacks:
Up Smash and Forward Smash have a Timed Hit mechanic. Release the button right when it finishes charging (before the shaking animation stops) to deal much more damage than usual. Stars will appear above Geno's head to indicate the timing of the charge, and the stars will disappear once fully charged. A sound effect will play if perfectly timed.
U-Smash- Geno lifts his hands up to charge, before bowing to the ground and summoning a Geno Blast pillar of light. Slower but stronger version of Palutena's Up-Smash.
F-Smash- Geno uses his signature move, Geno Beam. The beam is a multihit attack with long range, about half the length of FD, but with a long start-up time even if not charged up. Functionally similar to Mii Gunner's F-Smash, but with more range and longer start-up.
D-Smash- Geno fires a rocket punch low to the ground in both directions. His fastest Smash attack, but still relatively slow, and easy to avoid by jumping over.
Grab and throws:
When Geno has no hands, he can't grab, doing a 'whiff' animation where he looks confused. Pummelling has him fire stars point-blank from one arm. Up/Forward/Back throw all have Geno transform into a cannon a la Geno Flash and fire the opponent out of himself. Down throw is similar to Falco's down throw but with a star shot instead of a laser, obviously.
Specials:
Neutral B- Geno Whirl
Geno fires a projectile that travels quickly in a straight line. It pierces through players, high damage but low knockback, very slow attack. Timing a B press when it touches the opponent deals double damage. If items are turned on, then timing a B press for when the 'whirl' despawns (goes off-screen or touches a wall) will make it do 99.9% damage, but much less knockback to compensate.
Not very good for zoning due to its slowness and punishability on whiff. Great at long range for anti-zoning, or against slow opponents.
Side B- Star Gun
Geno fires his most powerful weapon, the Star Gun. This shoots a barrage of 4 stars that travel in a straight line with some variance in angle. Similar in frame data and damage/knockback to Falco's lasers if all four hit, but the stars move slower, allowing Geno to potentially chase after them and get a follow-up at certain ranges.
Up B- Geno Boost
Geno raises his hands to the sky for a moment (stalling mid-air) before given a "boost" upwards. While under the effect, Geno has stars below his feet, and he slowly rises, but he has complete control over his aerial moveset and left/right movement while rising. Not very good for vertical recovery, but GREAT for horizontal movement. The upwards momentum is cancelled upon jumping or airdodging, and ends after a few seconds. Geno must land on the ground to regain "fuel" for this move, similar to R.O.B. and Villager/Isabelle.
Down B- Geno Flash
Geno turns into a cannon and launches a star up and forward, which creates a multihit explosion as it expands. The explosion is similar to Hero's magic burst, but half the size. After the explosion, Geno appears in the center of it and then drops like a rock. If he's not above a platform after using this he's KO'd. Geno takes damage for using this move, too. (He literally blows himself up, after all.) Can be used as a recovery, but the cannon falls while it's firing, making its vertical distance pretty bad. Very high-risk high-reward move.
Final Smash- Star Road Beam
The camera zooms in to Geno's face as he prays, before the 7 pieces of the Star Road start to circle behind him... and then the 7 Star Spirits start to circle behind those (with Twink!), and then the 7 Crystal stars circle behind that. (Optional: The Pure Hearts also show up? Maybe the Bean Star? Something from other M&L games?) With the power of all the stars behind him, Geno flies up to the top of the screen and uses Geno Beam and Star Beam at the same time, creating a massive laser that destroys everything below him. He can be moved left/right slowly while firing. (Literally moves him, doesn't angle the laser like with Lucario.)
Taunts:
Up Taunt- The classic arms folded nod. Mallow also shows up to pose with him!
Side Taunt- Geno makes a pose similar to his 'guard' animation in-battle in SMRPG. "I serve... a higher authority."
Down Taunt- Geno trips and falls on his face, then stands back up and shakes his head quickly to shake it off. Coupled with the classic SMRPG sound effect.