I've seen what, 4 Greninja's ever since I started playing on For Glory? Meanwhile sometimes I face 3 Sheiks in a row.
I see these guys: Greninja, Ganondorf, Shulk, Ike, the Pits, Kirby, Jigglypuff, Yoshi, Sonic, Palutena, Lucario, Mr. Game & Watch, ZSS, Mega Man, Marth, Lucina, Bowser, and Duck Hunt more than Rosalina, Sheik, and Diddy. Add in the hodgepodge of Captain Falcon, Link, Little Mac, Toon Link, Mario, and Luigi - I just noticed they're all wearing either red or green, well, a red helmet in the Capt.'s case - and you've got the characters I see more than Rosalina, Sheik, and Diddy. Hell, I think I've seen more of Meta Knight, Dr. Mario, Charizard, Zelda, and Falco than those 4.
I've met like 4-5 Meta Knights and only one of them was amazing. This dude pulled off the Uairs to Shuttle Loop combo and would not give me a break. I've only fought one good Little Mac and that was near the game's release, two good Pikachus, and one good Peach. This leaves an issue where I don't know how to fight Rosalina, Sheik, and Diddy because I rarely see them. Same goes with Bowser Jr., Robin, DK, Peach, Wii Fit Trainer, Pac-Man, Wario, the Villager, Samus, ROB, and the Mii Fighters for obvious reasons.