Mine was a Pikmin vs. Pokémon Giant Heavy Metal w/Food only on the Halberd Brawl to the Squeak Squad theme!
That's a good question. It's been quite a while since I've played Brawl. Hmmm...
I think it was an Invisible match with 300% Damage, Metal and we were on the Rainbow Flying Boat stage. So all we were doing was jumping and instantly falling/dieing.
My one was an Invisible Heavy Metal Rumble Falls, so everybody just kept falling off the screen. I managed to survive by using my conniving plan: Luigi's recovery