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Raisins on a Rampage is a side mission in South Park: The Fractured But Whole.
This mission comes early on in the game. It is one of the simpler side missions in the game. After obtaining the Mosquito, you will need to defeat 15 Raisins Girls. They are mainly found just outside of Raisins, you can fight these foes whenever you like.
Completing this mission opens up the A Perky Predicament side quest.