You can easily gain Mojo by traveling through the three teleporters at Mount Grimly. Take the mutant you want to upgrade to the three teleporters. Get the Grimly that is respawning in the east and enter the left teleporter to Wumpa Island. Jump on the stone bridge thats on the left and walk south to Crash's house until you meet the Slap-Es. Slow down time and attack the Slap-Es with the Grimly's boxing attack. Keep attacking them to build up your Mojo multiplier. When all of them are defeated, teleport back to Mount Grimly. From there you can teleport to Wumpa Island again and repeat the process until you have a multiplier of 20. Back at Mount Grimly, take the teleporter in the middle that leads to the Wasteland. Once there you can destroy all the cactuses to get a large amount of Mojo. When there is no cacti remaining, teleport to Mount Grimly then go back to the Wasteland. All the cacti will be waiting for you again.