I know some brodudes. They are casual gamers, and I actually was curious to see what Brawl characters they actually recognized. These are people who started with the Super Nintendo/Sega Genesis and Nintendo 64/PlayStation, so the sample size may be different from what would happen with those who started gaming in with PS2/GCN/XBOX:
Sample one recognized: 23/39
Mario
Luigi
Bowser
Peach
Donkey Kong
Diddy Kong
Link
Zelda
Ganondorf
Samus
Yoshi
Kirby
Fox
Falco
Wolf
Pikachu
Jigglypuff
Squirtle
Ivysaur
Charizard
Wario
Olimar
Sonic
Sample 2: 23/39
Mario
Luigi
Bowser
Peach
Donkey Kong
Diddy Kong
Link
Zelda
Ganondorf
Toon Link
Samus
Yoshi
Kirby
Meta Knight
King Dedede
Fox
Pikachu
Jigglypuff
Squirtle
Ivysaur
Charizard
Wario
Sonic
Sample 3: 20/39
Mario
Luigi
Bowser
Peach
Donkey Kong
Diddy Kong
Link
Zelda
Ganondorf
Samus
Yoshi
Kirby
Fox
Pikachu
Jigglypuff
Squirtle
Ivysaur
Charizard
Wario
Sonic
Most casual players probably know who Mario, Luigi, Bowser, Peach, Donkey Kong, Link, Yoshi, Kirby, Pikachu, Wario, Sonic, and the original starters of Pokemon.
Of characters requested for Smash 4 the only ones I would say be recognizable to a "casual" gamer would be Toad, Bowser Jr., Waluigi, Mii, and Pac-Man. What's funny is that these casual players knew who Dixie Kong was over K. Rool, despite playing DKC1 and DKC2. Those that played Metroid were able to know who Ridley was though (though one simply called him "that Metroid dragon").