How to make characters have outlines; this is what you do:
In a modeling program, import the polygons that you want to have the outline. Copy the polygons, then make the copies bigger, until if you look at them, the original polygons are just fully inside the copied polygons. Have the copies' normals flipped, so that they're inside out. Have them textured to be a solid black color, and then import it in BrawlBox onto the character with "Import New Object".
SourceHow to do this + the 2D bit: I have no clue, but I do know this. Game&Watch's colors are in the form of palettes instead of textures, and so I don't believe the above technique will work in combination with the 2D effect.