When you first enter the castle, you will fight Kamek, and "kill" him. This, however, would make you accidently use stickers of high value due to the fact they were changed into flip-flops. I would recommend getting normal, weaker stickers to be turned into flip-flops. After you beat Kamek, leave the castle. Then, get as many powerful stickers as possible. (DO NOT use normal jumps! Bowser is a spiked enemy, so get iron jumps instead. Also try getting items that could damage multiple enemies.) This is what to do, along with the stickers:

  • First, get the stapler. It is able to staple the doors where minions go to help Bowser.
  • Then, get multiple cold-themed stickers, or a sponge. The cold stickers, such as Shaved Ice or Refrigerator, will help you against the Lava Bubbles that assist Bowser. The sponge could also help, as when Bowser attacks with the lava bubbles, the sponge would defend you.
  • You should also get lots of Baahammers. Near Phase 2, a chain chomp will appear. It's only weakness is being put to sleep.
  • During Phase 2, Bowser will be at full HP. Use your most damaging stickers here. I would recommend thing stickers and megaflash stickers. Remember the iron jumps, too!
  • By this point, Kersti would become a sticker. Use her, and you will get a spin combo of 5. Use your most powerful stickers here. (Also note the epic music.)

Bowser should be beaten, and you should get the Royal Sticker crown. Princess Peach would talk to you for a second, and then you would wish upon the royal sticker. You can't choose here, and it would bring Kersti back from the land of used stickers, if such a place exists. It would next show the Sticker Fest revival, where Bowser is about to do the same thing he did last time. However, Kersti appears to stop him. She says she might have to do that every year, and it ends. Many people would rage at this point, since it doesn't save and when you get back on the file it's right before you battle the final boss.