At the beginning of the level, jump on the "?" block (and maybe the "M" block to make it easier) and wall jump to the hidden area with a platform and a picture of Super Luigi from Super Mario Bros. crouching.
At the beginning of the level, jump on the "?" block (and maybe the "M" block to make it easier) and wall jump to the hidden area with a platform and a picture of Super Luigi from Super Mario Bros. crouching.