The cavern is characterised by bluish stone and a sandy floor thick enough for Petey Piranha to burrow and travel through. Additionally, the walls are covered with vines and rock formations that resemble the heads of Piranha Plants. There are also many openings in the ceiling, allowing light to pour inside, however the cavern is mostly dim. Dark Boos, Elite Boom Guys, and Snifaros are common enemies in this area. There are Monty Moles, as well, two of which run an Item Shop called the Monty Mart.
Mario, Luigi, Baby Mario, and Baby Luigi enter the Gritzy Caves through the floor of the Koopaseum. A group of Shroobs armed with powerful hammers surround them. They then strike the ground, making a hole which the bros. fall in. Soon afterwards, they encounter Kylie Koopa and a couple of Shroobs, only to see her fed to Petey Piranha - who, earlier, had also consumed Princess Peach - but before the bros. could do anything, the giant Piranha Plant burrows away.
After traversing through the cavern, the heroes finally battle Petey Piranha. Once defeated, he explodes and both Kylie and a Cobalt Star Shard fly out of him, but Princess Peach does not. Kylie explains that when she was eaten she saw the princess, however, Petey spat her out right after swallowing Kylie. The bros. proceed a little further to reach a dead end where they encounter the princess with a Shroob Mushroom on her face, and so they urgently return to the Mushroom Kingdom's present time.
. Dark Boo
. Petey Piranha (Gritzy Desert Boss)(Game Boss 3)