To beat the Final Trial and Emperor Bulbax (the big green guy in the arena) this is what you need to do:
1.Take out 30-90 blue pikmin and get half of them to work on each of the 2 bridges on either side of the stone wall
2.While the blue pikmin work, take out 10 red pikmin. Throw them on the ledge with all the flames coming up from the ground.They won't get burnt since they're red pikmin.Go into the water and call them with B so they follow where you walk, but they can't get off the ledge. Walk along the ledge so they get where the box is. They'll push the box out of the way and when they're done, dismiss them with X.
3. When the blue pikmin are done, put them back in their Onion. Take out at least 5 yellow pikmin and throw them on the land over the water on the right. Then bring them to the rock and throw them up to the bomb rocks so at least 3-5 have bomb rocks. Then get them back the same way you got them there, but when you call them back, just touch them so they don't drop their bombs. Then have them blow down the stone wall
4. take out at least 50 red pikmin and 20 yellow pikmin (including the yellow you took out) and have all your pikmin (including the yellows you took out) break down the white stick wall. You'll be in an arena with a big green thing in the middle DON'T TOUCH THE GREEN THING OR EMPEROR BULBAX WILL WAKE UP! YOU DON'T WANT THAT!...yet. Sneak past him and take down the white stick gate in the other side. Then there will be a whole bunch of cans with bomb rocks on the other side around the arena. Make sure all your yellow pikmin have bomb rocks.
5.Dismiss ALL your pikmin with X.Go wake up Emeror Bulbax and the leave to your pikmin, where he can't hurt you.Now walk slowly into the yellow pikmin so that you have one with you. Hold A so you can hold it and carry it with you. Now walk into all your red pikmin. Go back out to the Emperor. When he opens his mouth to lick up all your pikmin, throw the yellow pikmin with yor bomb rock and run off to the side. Your yellow pikmin will either land in front of him and get licked up, or land in his mouth and get swallowed, either way he will be swallowing a bomb. It will explode in his stomach and he will be stunned and he will lay down all dazed, looking like he's been drinking. THIS is when you have to throw all the red pikmin you can onto his FAT SAGGY CHEEK! When he gets up, call all your pikmin back and leave back to the other yellow pikmin. Keep doing this!
6. When half his health is gone, he will start jumping up really high and landing, killing all the pikmin who sadly get caught under all that FAT! make sure you use the Control Stick and the C stick to get the pikmin away from where he's going to land. He will do more jumpping than opening his moth to eat your yellow pikmin, but he will still do it, and that's still your cue to stun him!
7. When he is finally dead, he'll throw up the Secret Safe. You might not have enough time to carry it back, but even if you don't, just go to sunset and it will still be there when you get back.