As everyone here hopefully knows, Mr. Game & Watch has a fantastically low crouch. What you might not realize is that it has real defensive application; a large variety of moves simply cannot hit Mr. Game & Watch while he is crouching. I have tested every move from the ground with every character. In the case of specials, I do not make any claims about their ability to hit while the user is short hopping. All tests were also done on training mode; I don't know if that matters.
If I put a * next to a move, that means it can hit a crouching Mr. Game & Watch if it is angled downward. With many tilts and smashes, the users of the moves frequently do not angle the attacks making crouching a fairly viable defense.
Mario:
nothing
Luigi:
Fire Jump Punch (up special always lands weak hit)
Peach:
up tilt
standing grab
running grab
Peach Bomber (forward special)
jab (beam sword)
Bowser:
up tilt front side (back can hit)
Donkey Kong:
up smash
Diddy Kong:
Peanut Popgun close range (neutral special)
Monkey Flip grab (forward special, far range kick can hit)
Yoshi:
up smash
running grab
Wario:
nothing
Link:
Gale Boomerang outgoing*
Bow close range (forward special)
Spin Attack (up special)
Zelda:
jab
forward tilt*
up tilt
up smash
Sheik:
jab first hit
Ganondorf:
jab
forward tilt
forward smash*
standing grab
running grab
Warlock Punch (neutral special)
Warlock Kick (down special)
Toon Link:
Bow close range (forward special)
Samus:
jab first hit
forward tilt*
forward smash*
up smash
Charge Shot any charge except full (neutral special)
Super Missiles (forward smash special)
Zero Suit Samus:
jab first hit
forward tilt*
up tilt
standing grab (except at max range)
running grab (except at max range)
Paralyzer (neutral special)
Pit:
Palutena's Arrow (neutral special)*
Ice Climbers:
nothing
R.O.B.:
jab first hit
forward tilt*
forward smash*
up smash
Robo Beam far range (neutral special)*
Kirby:
nothing
Meta Knight:
up smash
King Dedede:
up tilt
Waddle Dee Toss close range (forward special)
Olimar:
up tilt
Fox:
jab first hit
Blaster (neutral special)
Falco:
Blaster (neutral special)
Reflector (down special)
Wolf:
nothing
Captain Falcon
jab combo (excluding rapid punch sequence)
forward tilt*
forward smash*
standing grab
Falcon Punch (neutral special)
Falcon Dive (up special)
Pikachu:
nothing
Squirtle:
nothing
Ivysaur:
Vine Whip (up special)
Charizard:
up tilt
Lucario:
up smash
Force Palm grab (forward special, blast can hit)
Jigglypuff:
nothing
Marth:
up tilt
Dancing Blade hits 2 and 4 up (forward special: unsure if I'm right here)
Ike:
jab first hit
Ness:
up tilt
Lucas:
nothing
Mr. Game & Watch:
up tilt
Fire (up special)
Snake:
jab combo
Nikita Missile (forward special)*
Sonic:
nothing, but by crouching under a spring on the ground, Mr. Game & Watch is safe from all aerials
If I put a * next to a move, that means it can hit a crouching Mr. Game & Watch if it is angled downward. With many tilts and smashes, the users of the moves frequently do not angle the attacks making crouching a fairly viable defense.
Mario:
nothing
Luigi:
Fire Jump Punch (up special always lands weak hit)
Peach:
up tilt
standing grab
running grab
Peach Bomber (forward special)
jab (beam sword)
Bowser:
up tilt front side (back can hit)
Donkey Kong:
up smash
Diddy Kong:
Peanut Popgun close range (neutral special)
Monkey Flip grab (forward special, far range kick can hit)
Yoshi:
up smash
running grab
Wario:
nothing
Link:
Gale Boomerang outgoing*
Bow close range (forward special)
Spin Attack (up special)
Zelda:
jab
forward tilt*
up tilt
up smash
Sheik:
jab first hit
Ganondorf:
jab
forward tilt
forward smash*
standing grab
running grab
Warlock Punch (neutral special)
Warlock Kick (down special)
Toon Link:
Bow close range (forward special)
Samus:
jab first hit
forward tilt*
forward smash*
up smash
Charge Shot any charge except full (neutral special)
Super Missiles (forward smash special)
Zero Suit Samus:
jab first hit
forward tilt*
up tilt
standing grab (except at max range)
running grab (except at max range)
Paralyzer (neutral special)
Pit:
Palutena's Arrow (neutral special)*
Ice Climbers:
nothing
R.O.B.:
jab first hit
forward tilt*
forward smash*
up smash
Robo Beam far range (neutral special)*
Kirby:
nothing
Meta Knight:
up smash
King Dedede:
up tilt
Waddle Dee Toss close range (forward special)
Olimar:
up tilt
Fox:
jab first hit
Blaster (neutral special)
Falco:
Blaster (neutral special)
Reflector (down special)
Wolf:
nothing
Captain Falcon
jab combo (excluding rapid punch sequence)
forward tilt*
forward smash*
standing grab
Falcon Punch (neutral special)
Falcon Dive (up special)
Pikachu:
nothing
Squirtle:
nothing
Ivysaur:
Vine Whip (up special)
Charizard:
up tilt
Lucario:
up smash
Force Palm grab (forward special, blast can hit)
Jigglypuff:
nothing
Marth:
up tilt
Dancing Blade hits 2 and 4 up (forward special: unsure if I'm right here)
Ike:
jab first hit
Ness:
up tilt
Lucas:
nothing
Mr. Game & Watch:
up tilt
Fire (up special)
Snake:
jab combo
Nikita Missile (forward special)*
Sonic:
nothing, but by crouching under a spring on the ground, Mr. Game & Watch is safe from all aerials