* Nintendo chooses what amiibos are made. Centralized.
* There are many copies of a small number of amiibo types. Fungible.
* You get a physical thing. Not a token
* Only nintendo games may use amiibos
* The data on the amiibo is uniquely interpreted for each game. It's not a generic interface. Not all amiibos will do anything to every game.
Amiibo, and pokemon (trading the pokemon) are great examples of how to trade and scale information exchanges in the real world without needing an NFT blockchain. Blockchains are terrible ideas for games.
The point I was getting at was that udbhavs' comment on "no two games would ever want to share an item" reminded me of a case where several games do share some item, though in this case not a unique one. Any item shared between games would always have to be interpreted by each game unless they're based on some shared engine feature or module for interpreting them.
As an example, I have the Twilight Princess Link Amiibo. In most games it gives some reward related to The Legend of Zelda in general. When I scanned it in "Yoshi's Woolly World" for the Wii U it unlocked a Yoshi looking like Link, as would any Zelda themed Amiibo. When I scanned it in The Legend of Zelda: Breath of the Wild for the Switch it instead unlocked Epona, Link's horse featured in many games, including Twilight Princess. Which can only be unlocked by that specific Amiibo and no other Zelda ones.
Of course, these tags are not unique and can quite easily be cloned.