the perplexing pool is the third area in pikmin 2. there is one onion, and... one to two new pikmin types, depending on how you feel about bulbmin
i think your old enough to explore this area on your own :3 thats right im giving YOU permission to actually play pikmin
to get to the yellow pikmin, bring as many whites as you can and lots and lots of reds. idealy you should fight the firey bulblax with bitter spray, but spicy works too if you have like 80 reds. you shouldn't bring 80 reds, though.
this area has four caves - the citadel of spiders, the shower room, the glutton's kitchen, and the submerged castle. so fun ^_^