World 1: Iggy Koopa

Beat up Iggy Koopa: You must battle Iggy Koopa on
 an island tilting in molten lava. He attacks in one way
 only. He will climb into his shell and roll a ball at you.
 To beat this not-very-scary attack, just wait until the
 island tilts to the right and then jump on his head two or
 three times. If he gets knocked back on then just keep
 trying to knock him off again. If you do it right then Iggy
 Koopa will roll into the lava.