Hey Nash, how did you unlock Luigi? And what was that move (I think you did it) where a big green dome appeared? I hadn't seen that one yet.
I was playing the regular multiplayer brawl matches against my bro, and I think after 22 of them you can challenge him, then when you beat him you get him in your roster. Just play the multiplayer against the cpu and set the rules to "stocks" and set the stock to 1 only. Then just fall off the cliff right away.
check out this site for all the tips on how to unlock characters.
https://www.gamefaqs.com/console/wii/code/928518.html
as for the green dome thing, i have no idea! i dont even remember doing it.