Mario and Luigi Comparison
Jab: Luigi has more range and gives up to 10%, as opposed to Mario's 9% maximum. Mario's might be a bit faster, though.
F-Tilt: Luigi has slightly longer reach, but is a touch laggier.
D-Tilt: Luigi has less raneg, but more power and a chance of tripping his foe
U-Tilt: Luigi doesn't juggle quite as easily, but once again has more power
F-Smash: Mario's got more range and power (if sweetspotted), but Luigi's attack is faster
U-Smash: Mario is said to have more range here
D-Smash: Mario's got more range, slightly less strength. Mario's might be a bit faster...
N-air: Luigi's has better power, knockback, and killing potential. Better move overall.
F-air: Mario's is stronger and can spike, but is slower.
B-air: Pretty much the same, with Luigi having a touch more range.
U-air: Pretty much the same, with Luigi having more power
D-air: Luigi's can spike, but is hard to master. Mario's is better for approaches and packs more punch.
Grabs: Pretty much all even.
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Speed: Mario runs faster, and is probably the faster-paced character overall
Range: Luigi wins here, with longer legs
Power: Mario and Luigi are about tied here, with luigi being a touch stronger
Aerial: They're about tied here. Mario may be a bit better.
Ground: Depends.
Recovery: Luigi wins.
Edgeguarding: We should all know this.