You have Diddy and Dixie, and you must get into the up arrow barrel above Kannon ( the guy holding the cannon ). How are you able do this?
 

Switch to Dixie, spin over the cannonball and onto Kannon's head.

Jump over the cannonball, cartwheel into Kannon and go into the barrel.

Duck as the cannonball passes, jump on Kannon and into the barrel.