Instructions
Defeat the first boss, Dodonga, to get the "Chaka" drum. Go to the hunting plain, then repeat the rhythm shown on the totem pole (Triangle --- Circle --- Triangle --- Circle) three times to make the totem grow and spit out a compass.
Navigate to the stage select, the Compass has opened up a new map called "Miracle of Lostdon!" At the end of this stage is a larger version of Dodonga called Majidonga. Defeat it and you'll receive the "Don" drum and the ability to play the Rain Juju.
Go to the "Desert Crossing" stage and advance until you get "Fever" mode. Once in Fever mode, activate the Rain Juju by pressing "X --- XX --- XX" which puts you in a special call and response mode that you have to complete to start the rain. Pay attention to the rhythm the Patapon call out, because you'll need to match it.