A New England Winter
Smash Lord
See, now I like that idea. Eevee would work best like that, definitelyI love Eevee and Flareon and Jolteon and Vaporeon and Umbreon and Espeon and Leafeon and Glaceon. That would be a great pokeball, Eevee comes out and evolves into one of his forms and attacks.
As for playable, I'd go with Lucario, Scizor, Blaziken and/or Pichu Bros./Plusle&Minun
Lucario because it has such awesome, original and unique techniques to use, it's actually a Fighting type, it's got a movie based on it, it's famous and FREAKIN' AWESOME...what more is there? It's almost perfect for a fighting game. No other Pokemon needs to be in as much as Lucario. I'd main him in a second.
Scizor because he, like Lucario, is a very unique, very powerful Pokemon who could act as the next Fox (high speed, fast falling), but also heavyish, with slow ending moves that start fast. It could also be able to glide, and have excelling air combat. Although it's kinda hard to see Scizor in a Brawl match...but cool nonetheless...
Blaziken. He's awesome. Need I say more? Sky Uppercut. Blaze Kick. Brave Bird. If this isn't a Brawl worthy Pokemon, I'd be hard pressed to think of another. This would make his popularity rocket to the FREAKIN' MOON. He'd be the new Captain Falcon, albeit faster with better jumping skill, and lighter weight. Highly recommended. I'd also main Blaziken in a second.
Pichu Bros./Plusle&Minun would replace Pichu, and be kind of like Ice Climbers on speed, much lighter, and electrical. They'd have attacks based on the two of them, but instead of just simultaneous attacks, they'd have successive attacks. Example would be pressing B to do Thundershock, and pressing it rapidly would produce one after another successively, but slowly so as to not be super broken. It's kinda hard to imagine them in action, but I'd play them once or twice...