Heres the list and I'm positive that this is all of them.
1. Large Prinna Plant with two cages (Mario sunshine)
2. Rayqeuza (Pokemon)
3. Porky, large robot (Earthbound mother 3)
4. Duon, large 2 sided robot (Custom)
5. Master hand (Custom) only in boss battle mode
6. Crazy Hand (Custom) only in boss battle mode
7. Gollem, A tank robot (Custom)
8. Ridley (Metroid)
9. Metal Ridley (Metroid zero mission)
10. Tabu, final boss (Custom)
you dont
In Boss Battles, there are 10 bosses.
None of them are playable characters.
None of the bosses including tabuu can be played.
You can't play as the bosses.
All bosses including taboo are unplayable.
None of the bosses including tabuu can be played.
Super Smash Bros., Super Smash Bros. Melee, Super Smash Bros. Brawl, Super Smash Bros. for Nintendo 3DS/ Super Smash Bros. for Wii U, Super Smash Bros. Ultimate.
You can only install Super Smash Bros. Brawl on your Wii with a Super Smash Bros. Brawl disc.
No he's a boss and bosses don't become characters
Yes you can! You can be tabuu and crazy hand(not master hand)
The "sequel" to Super Smash Bros. Brawl, in a way, is Super Smash Bros. for Nintendo 3DS/Super Smash Bros. for Wii U.