PIRAHNA PLANT: This guy reminds me of Andross... He'll start by trying to suck you up, press A repeatedly to stay above his mouth. He will also eat two bomb seeds. He will then spit out his Bomb Seeds, grab one with B and dodge the other. DO NOT THROW IT YET! Throw it in when he tries to suck you up again, and he'll lose one hitpoint. Repeat the process, except watch out because he sucks you in faster and eats three bombs. After you hit him again, he sucks you up superfast and gets four seeds. Now show that chump not to mess with Wiggler!
HAMMER BRO: Should have been before Pirahna Plant, because this guy is easy. Just copy his notes. He starts by hitting his drums 3 times, then 4 and then 5 after you start hitting him. Very easy indeed.
DRY BONES: A very interesting way to beat Dry Bones. Normally I hit him with a cape or a couple Red Shells. Anyway, first pound the switch highlighted by a fire symbol. A magic blast will hit Dry Bones. Then hit the next two switches in the order indicated on the top screen. Two magic blasts hit Dry Bones. Now just basically do that with three switches and Dry Bones will be Broken Bones.
KAMEK: Argh, I'm reminded of those times in Yoshi's Island where Kamek was such a pain... Anyway, the moron will teleport you to a hallway. Play a little game of Galaxian with his books and bookcases, then get to Kamek. Kamek will start throwing those Koopa Spells at you. Dodge those and hit him in the face with ink until it's completely covered, then get to the middle. Kamek will fire spells in every direction, then some books will fall down. Dodge those, then get out of the middle as Kamek gets hit in the head by a very big book (that's one way words can hurt you). Repeat the process, except Kamek will this time fire two spells at once, and make a wall of books attack you. After inking up his face again, he will get hit with another book. Repeat, except this time, after his two book walls, he will send two books out to get on both sides of you and smash you. Once you inkatize his face again, he will go berserk with spells, and then his blue dictionary will KO him. Phew...
BOWSER: Bowser will put on his Megamorph belt and turn into a golden Bowser Block. Black Bowser Blocks will form a top, and the golden block is on the side. Avoid the "Bey-Bowser" by running in circles around the edge (at least, that's what I do) until he slows and stops. If the Golden block is near the ground you can punch it. If it isn't, jump-kick it. When you hit it enough (5 hits should do it), Bowser will turn into his Block form. Wait for the Block to move (in a Tox Box like manner) and stand by his corner until fireballs come out, then punch the weak point till he turns over or goes to his next form, the Snake form. Dodge the snake until it shoots fireballs, then go to the middle. Have the snake run at you, and punch its head (just keep punching, don't worry about getting hit) until Bowser is defeated. This is the toughest boss of all.