Mummipokey

Mummipokey is the second boss in New Super Mario Bros.

Mummipokey is a mummified Pokey, who is a vertical, spikey caterpillar.

In this battle, Mummipokey pops up at different heights and places. Mario or Luigi must wall jump on his head, 3 times to access world 3.

However, if you want to get fancy about it and access world 4, you can defeat him as Mini Mario. You must ground pound his head 3 times as mini mario to access world 4.