I've always wondered why there's never been a proper Game Boy rep in Smash, but now I think about it there's only really two realistically viable options: Muddy Mole and Prince of Sablé.
Who Are You Running From? is based on a real guy
Warlocked technically isn't Nintendo, and never released in Japan
Alice would more likely than not be passed up in favour of the more recognisable Balloon Fighter
Tatanga is an obscure rep for a well known IP
Yakuman Player is well... Yakuman Player.
X has no real characters to draw from
I should note that Kakrurenbo Battle Monster Tactics is a bit of an outlier, since I can't find much English info about it. There could be stuff to work with, there could not, but what I can find about it doesn't make it sound very interesting.