After beating the subspace emissary you will unlock a boss battles mode go under Solo and Stadium then choose the boss battles mode in this mode you must face off with all 10 bosses one by one you can choose to use a heart container once your weak.
By boss mode im assuming you mean all-star and it must be in Super smash brothers melee You have to unlock all the characters.
of hole
You have to beat every boss in boss mode with fox and then defeat wolf!
A boss in the Subspace Emissary (Adventure Mode in Super Smash Bros. Brawl)
Yes, he is the final boss in the SUper Smash Bros Brawl story mode, but he is not a playable character.
To unlock Boss Battle Mode which is located in Stadium in Solo Mode you have to beat the Subspace Emissary.
for the trophy just beat boss battles on easy mode
He will appear right before you get to the final boss fight.
BRAWL
SSE is an abbreviation for Subspace Emissary, Super Smash Bros Brawl's adventure mode.
I am pretty sure you can only face him in boss battle mode. sorry.
Vs mode and brawl are the same thing.
All bosses can be battled either in the subspace emissary or boss battle mode.
its the story mode