I need help with unlocking Boss Rush, I read I had to have the MPO original save on my memory. I have this yet I still don't have Boss Rush. Am I supposed to wait until I complete Extreme Mode on MPO+ or do I suppose to complete all of MPO original, because I haven't yet.

Your help is greatly appreciated, and thank you in advance.

I think you're suppose to have a MPO game save which is completed at least once.

you can also download a copy of an MPO save on GAMEFAQS

So while we're on the topic, what's the deal? I got to cunningham, had 2 guys left, and couldn't pick one when i died. I could pick a new one at RAXA and PYTHON, why not here?

Remember from the first game, you could ONLY have one soldier fight Cunningham and Gene. That's just how it is, but only for those two bosses (Consider it a 1vs1 battle).