Stamp

Stamps are collectibles found in many Wii U games. They are earned by completing certain in-game tasks, and could be used on handwritten Miiverse posts prior to the service's termination on November 7, 2017.

Super Mario 3D World / Super Mario 3D World + Bowser's Fury
Stamps first appear in Super Mario 3D World and reappear in its Nintendo Switch port Super Mario 3D World + Bowser's Fury. There are 85 stamps in this game. 80 of them are scattered in courses or Sprixie Houses, while the other five are gained by completing every course with any character (one gained per character). All the main courses in the game (with the exceptions of the courses in World Mushroom and World Flower), and all Sprixie Houses have one Stamp in them. While Stamps are normally not in Captain Toad's Adventures courses or Mystery Houses, the ones in World Crown have them.

In the Nintendo Switch version, Super Mario 3D World + Bowser's Fury, Stamps are in color and repurposed to be used with the new Super Mario Odyssey-styled Snapshot Mode, where they can be pasted onto the environment.

Super Mario Maker
Stamps appear in Super Mario Maker. In this game, they are available by default, and no in-game tasks are required to unlock them.

NES Remix
Stamps make their second appearance in NES Remix, where there are 100 Stamps in it. They are gained by obtaining enough Bits. Ten are unlocked from the start, while 90 must be unlocked.

NES Remix 2
In the sequel NES Remix 2 they appear once more, and like in the previous game, there are 100 Stamps, but none of them are unlocked from the start. 95 of them are earned by obtaining Bits, while the other five are unlocked by completing certain challenges.

Mario Kart 8
Stamps also appeared in Mario Kart 8 and in this game, there are 100 Stamps, but 28 of them are unlocked from the start. 30 of them are earned by playing a Grand Prix race (one per character), and the other 32 are unlocked for beating a Staff Ghost in Time Trials (one per course). In addition, ten more stamps were added if they purchase both DLC packs. Stamps have been removed from Mario Kart 8 Deluxe, with completing a Staff ghost on 150cc no longer unlocking them.

Mario vs. Donkey Kong: Tipping Stars
Stamps appear in Mario vs. Donkey Kong: Tipping Stars. One way of getting those is by buying items in the Workshop Store. Over 70 stamps can be collected.

Yoshi's Woolly World
Stamps appear in Yoshi's Woolly World. In this game, every level hides 20 Stamp Patches inside beads, the game's collectable currency. Collecting a certain amount of these Stamp Patches will earn the player five new stamps. When a Stamp Patch is collected, the player will be able to see a stamp icon on the beads they collected them from, whenever they replay the level. There are 70 stamps in total to collect.

Mario & Sonic at the Rio 2016 Olympic Games
Stamps appear in Mario & Sonic at the Rio 2016 Olympic Games. In this game, there are 100 stamps for players to collect.

Super Mario 3D World

 * Instruction manual bio: "You can use the stamps you collect in your Miiverse posts."