After collecting all four Trophies from The Lost Ruins, you'll face Papu Papu. This boss battle takes place on a modified version of Papu's Pyramid. Papu Papu's main attack involves dropping green beakers and occasionally a red beaker.
Phase 1: Green Beakers
Papu Papu will primarily drop green beakers, which cause you to spin out if you drive over them. He drops them in clusters, making it difficult to navigate. Your goal is to avoid these beakers while maintaining your speed. Use power slides to weave through the gaps. He will also occasionally drop a single red beaker, which is more dangerous as it homes in on you. If you get a shield, save it for when a red beaker is incoming.
Phase 2: Increased Beakers & Red Beakers
As the race progresses, Papu Papu will drop more beakers, and the frequency of red beakers will increase. He'll also start dropping them in more strategic locations, often on the racing line or just after a jump. The key to beating Papu Papu is to stay ahead of him and avoid his traps. If you fall behind, it becomes much harder to navigate the minefield of beakers. Use your mini-turbos consistently and take advantage of any speed pads on the track. Winning this race unlocks the next hub world, Glacier Park.