Olimar isn't really needed though, and it just makes more players rely on one specific player playing correctly, where if it's all pikmin if one player isn't playing correctly he doesn't screw everyone else up as much.
One possible way to do it:
Players could have 4 item slots, with 4 different actions.
1. Carry: The action that is used to help carry pellets and dead enemies. I'm not quite sure how this should work, but that can be worked out when it is time for it to be implemented. Also used to push pushable obstacles out of the way.
2. Attack: The Brikmin flails his arms ( rapped clicking animation) just like pikmin do.
3. Throw: The Brikmin can pick up Pikmin that want to be thrown (see bellow) and throw them just like Olimar did. Used to reach high places and get over small obstacles so that the Brikmin can open the way for the rest.
4: Throw me: Put arms up into the air, and allows fellow Brikmin to pick them up and throw them.
Additionally, each colored Brikmin would have special benefits:
-Red are fireproof.
-Yellow have an extra inventory slot so they can pick up and drop bombs, and are thrown farther and higher.
-Blue can go into water without dying.
The game could start with say 50 red Pikmin. Whenever someone spawns, they take out one Pikmin from an Onion. Players have to gather more pellets and food than they die, otherwise all the Pikmin are wiped out and players lose. The players would start at an easy level, and after a few rounds (or possibly collecting all of artifacts or something) the next day they arrive at a harder level. As the levels progress, more teamwork will be needed, and the Brikmin's specific abilities will become very important, causing players to work together and switch out Brikmin types frequently. On later levels there could be flowers that when the player jumps in they convert to that color just like in the game.
Thoughts on what I just said?
I (we) should make a single player pikmin mode =3
Go play the game. No reason to reinvent the wheel.