Here are all the bosses in the game
World 1 Boss: Iggy Koopa: A hit from a hammer can defeat him.
World 2 Boss: Morton Koopa Jr: he faces the direction you are facing, defeat him with 2 shots of fire
World 3 Boss; Lemmy Koopa: Kick him off the bouncy ball 3 times.
World 4 boss: Ledwig Von Koopa: He spits fireballs, use blocks to hit him with a hammer shot or fireball.
World 5 boss: Roy Koopa: the only koopaling to be changed, he has a spike on his head, so you can only defeat him with tanooki mario or fire mario.
World 6 boss: Wendy O Koopa: trick her fall into falling the lava, the pow can break the bridge she is on.
World 7 boss: larry Koopa: he controls a bill blaster, use the bill blaster to defeat him.
World 8 boss: Dark Bowser/Giant Dark bowser/Mega dark bowser/biggest dark bowser: all you need to do his hit him with a shell and he will grow. he will atempt to grow bigger than mars but explodes.