From the Super Mario Wiki
The Royal Stickers are six special stickers that first appear in Paper Mario: Sticker Star. Kersti is their guardian, and they appear to form the Sticker Comet. Royal Stickers can grant wishes and give power to the people who wield them, which may also alter their personality.
Paper Mario: Sticker Star
On the night of the Sticker Fest, Bowser touched the Sticker Comet and scattered the Royal Stickers across the lands. Mario and Kersti travel to five lands to reclaim the stickers: the grasslands of World 1, the sunbaked desert of World 2, the dark woods of World 3, the snowy mountain of World 4, and the volcanic island of World 5, battling Bowser's minions to save the five Royal Stickers. The final and most powerful sticker lands on Bowser's head and grants him amazing power.
The bosses guarding the other 5 are Megasparkle Goomba (World 1), Tower Power Pokey (World 2), Gooper Blooper (World 3), Mizzter Blizzard (World 4), and Petey Piranha (World 5). Each boss has a rhyming story about their background before they received the Sticker, as well as how they got it. Once a boss is defeated, Mario must pick up the Royal Sticker to complete the world and move on to the next.
The Royal stickers make a few cameo appearances in Mario & Luigi: Paper Jam. The red Royal Sticker's likeness is used in the design of the Megacrinkle Goomba Papercraft, which seems to have been designed after the similarly named Megasparkle Goomba. Later, the trio of Mario, Luigi and Paper Mario fight Big Pokey and Tower Power Pokey as bosses; the Tower Power Pokey appears to be wearing the second Royal Sticker once again, with the orange gem on top replaced by an orange spike.
The final Royal Sticker also appears on a Battle Card, being worn by Shiny Paper Bowser.
List of Royal Stickers
Names in other languages