the problem is that if the enemies are smart enough to take control of the banana game, and if diddy sucks at banana game (player in general duh) then your team work been cut half or even more and you'll be sent straight to devil's son and have a bad spanking from him lol.
Oh Noes @_@, anything but that! Well its always a good idea to team with a diddy that knows how to use the bananas, and seriously though, my friend and I play in a certain way when it comes to doubles. We alternate sides: one person is always in the air, the other is always on the ground. Or, one person is in the air on the left side, the other on the right. Or, both of us on opposite sides. It sounds kinda stupid, but by spacing yourself, you won't have to worry about losing bananas when they are thrown. An example:
Lets say a match starts on FD and the characters spawn in this order: Luigi, Diddy, Enemy1, and Enemy2. Diddy pulls a banana while Luigi does a rising dair (or w.e) to grab it. Diddy does a dash attack through Enemy1 and does a RAR bair while Luigi throws the banana forward. It hits Enemy2 which protects Diddy's back. Luigi lands near Enemy1 and proceeds with a buffered ShieldGrab or something, throwing Enemy1 away. Diddy hits Enemy2, grabs the banana and throws it to Luigi, who glidetosses it back to Enemy1.
Yeah it sounds situational and unlikely to happen, but think of it like playing any team sport: you watch your teammates and coordinate your movements with theirs. I'll contact the Diddy i teamed with and make a couple videos showing some of this stuff done. Because of the banana game, Diddy is one of the best teammates, but his abilities can be exploited further if Luigi is on his team.