Instructions
Select the castle stage on the right side of the World 2 map.
Play through the castle until you reach a rope hanging above a large spiked ball near the end of the level. Jump onto the rope and swing onto the platform to your right.
Jump under the second question mark block. A blue miniature mushroom appears. Touch this mushroom to transform into Mini Mario.
Navigate to the right and enter the large wooden door to be taken to the chambers of the World 2 boss.
Damage the boss, Mummy Pokey, by jumping over his head and pressing "Down" and "B" to perform Mario's ground stomp attack on the head of the boss. Mummy Pokey flashes red to indicate he has received damage. Only ground stomps affect him while you are Mini Mario. Avoid the fireballs the boss shoots by jumping over them.
Damage the boss three times over the course of the battle to defeat him. Mario automatically walks to the right once Mummy Pokey is defeated. However, Mario falls through the tiny gap in the floor, due to being Mini Mario, and is transported to World 4.