All this talk about great 3rd party characters, and me finding my N64 after the move, got me to play this game. A lot. A loooooot. So lemme do my usual FlipTroopa magic, eh?
Firstly, the game was co-developed by Treasure and Enix, then published by Enix in Japan, and Nintendo in the US. But Nintendo publishes a lot of games, like Mega Man 6, so that doesn't make a difference. Likely they would need permission from Treasure and Squeenix to use the character.
Marina has appeared in TWO games. The second was a really weird PSX fighting game called Rakugaki Showtime. Look it up: it's a messed up game, very similar to Smash Bros. if it was handdrawn with original characters. It even has its own boss, God Hand (as opposed to Master Hand), who draws all the fighters and items. Funky.
Anyways, Mischief Makers was the best-selling Treasure game in the US, and probably the only with mainstream presence. Everybody who had a N64 at least rented or knew somebody who rented this game. It's one of Treasure's more popular titles in Japan as well, up there with Gunstar Heroes and Radiant Silvergun.
That moveset for Marina , btw, is alright, but I would've liked more originality in the B moves. She has the Shake power, but she should get a few other abilities as well. I was picturing maybe her neutral B just being her basic Shake skill from the actual game, where she can catch people and toss them in any direction or shake them for minor damage. She could potentially grab and shake items this way as well, maybe making them more powerful? (that's her main ability in Rakugaki) Her Forward B I pictured being like the Raptor Boost, and then I could see her getting some unique abilities for the other two. Like an earth shaking or clanbomb making attack for Down B, and some crazy hover skill for Up B. Btw, if they add airdashes in Brawl, this is the perfect character for it.