Paper Mario: Sticker Star

If you paperize the area around a circle of flippable flowers, you will see a stickable area appear. Stick a sticker and a "?" block will appear. Inside the block will be a more powerful version of the sticker you originally stuck.

Obtain three flasy fire/ice flowers and make your way to World 1-2. Grab the fan and find the area where the Toad is crying. Paperize the flowers and place them on the field where indicated to receive twice the number of flowers. Now you can sell the duplicates and also the fan, then repeat the process as often as you like for easy flashy fire/ice flowers and coins.

Collect all 96 battle stickers.

Once you place all of the Battle Stickers in the museum, a new door appears. Pass through it and you'll find that if you pay a single coin, you get to see enemies attacking a cutout of Mario. Various animations will display as those enemies attack.

If you find Luigi five times while playing through the game, he'll appear at the start of the end credits, holding the banner. The locations where you can find Luigi are as follows.