It's really just a matter of leveling up and getting at least average battle power....if you have a good team you'll be able to finish all of them + all bonuses without even losing a single ninja, every single day....been doing so for weeks now. Don't forget...the enemy teams are on auto mode without a human brain behind them, and 90% of them still include the crappy Tobi....it's easier now than it ever was to be honest...