Man, having Geno in Brawl would be a dream come true for me. I love SMRPG LotSS. It was the best of the Mario RPGs that have been made. Anyway I'll throw in my 2 cents for a moveset that could be made for him.
I think Geno should break the mold a little. He should be pretty powerful, however be very light and easy to knock away.
Size: 2.5 (think Ness)
Weight: 1.5 (he's made of wood, what do you expect?)
Speed: 3.5 (above average)
Power: 4 (despite being small, Geno should pack a punch!)
Jump: 3 (again, just average)
Entrance pose: A small star decends from above in a zig zag pattern then materializes into Geno. He looks toward the camera and strikes a cool pose.
Regular Moves
A - A quick right punch
A, A - A quick follow up with his left
A ^ - Geno jumps up and headbutts.
A -> - A swift mid kick that causes Geno to spin around
A v - A very quick, but weak low kick.
Dash A - Geno jumps forward and does a front flip that turns into a drop kick.
Smashes
A ^ - Geno crouches, then jumps up and shoots his arms out above him a little ways, then they return to him.
A -> Geno pauses for a bit, then he shoots both his arms out. They travel a short distance then return to him.
A v - Geno shoots both his arms out as he crouches down low. His arms travel around his body in a circular motion to knock away any close opponents, then return to him.
Air
A - Geno twirls his body around.
UA - Geno does a backflip, and his legs will smack anyone above him away.
FA - Geno sticks both his arms out in front of him.
DA - He pauses for a second then takes both his arms to spike an opponent downwards
BA - A short, but powerful rear kick.
Grabs
Attack - Geno pumps his victim full of star bullets.
U - Geno tosses his opponent up high and blasts star bullets at them.
F - He does a flip, then tosses the opponent into the air.
D - Geno stomps repeadiately on his victim, then kicks them away.
B - Geno tosses the victim over his head and shoots many star bullets at them.
Special Moves
B - Geno Beam - As you hold down the B button Geno will start to glow. As you hold B down, the beam will get more powerful. When Geno has sparks flying from him and starts shaking, the beam will be the most powerful if you release B. However if you wait too long after Geno starts shaking, the beam will misfire and you'll do a little damage to yourself. When the beam is fired, its thickness is dependant on how long you held B. When released a beam of energy will travel straight forward the way you're facing. The beam causes multiple hits on an opponent, but lacks knock out capabilities.
B -> - Geno Whirl - Holding the button down, Geno will charge a disk of energy (think destructo disk DBZ style.) Just like using the Geno Beam, when you see sparks and he shakes, it's the best time to throw it or else he'll damage himself. When released Geno will throw an energy disk. It works like Link's boomerang, and you are able to aim it. However it doesn't come back to you, but instead will keep going in the direction it was fired. When it hits a solid surface or an enemy it will bounce off it. Depending on how long you held B, the disk will be larger. But no matter what it will still disappear after around 2 seconds.
B ^ - Geno Boost - Geno rises sharply upward while spinning around. You can slightly control the horizontal movement. Does rapid, but light damage to enemies.
B v - Geno Blast - Just like Beam and whirl, hold down B to charge power, but don't overcharge. When released Geno will call down multicolored beams from above. How many depends on how long you held B. Just like Pikachu's Thunder, any platforms would block the attack.
Taunt: Crosses his arms, turns his body to the side, and looks to the camera.
Super Smash Attack: Geno turns into a cannon, and energy starts to charge up. While this is happening you can control the angle of the cannon and which way the shot is fired. When done charging a ball of light will pop out, and if you press a button an explosion will occur. Its radius is small, but it does a lot of damage to those in the way. Doesn't KO however.
Phew! I'm done.