Paper Mario: Sticker Star Easter eggs

I-Up Sticker at Drybake Desert
While playing the Drybake Desert map progress through until you come to the big sand waterfall with all of the Pokeys to avoid. Progress up until you see a relatively small island with one single Spiky Pokey on it. Head here and investigate the rocks that look like the back of the screen (just the brown small ones on the island), and you should find a secret entrance. After going inside you will be in a secret area with coins and a ? Block. Hit the block to get the 1-UP sticker.

Note: The entrance is to the right so go right up against the rocks and head right along them.