How much game data can I store on an amiibo at any one time?
You can store game data for a single game that uses the read/write functionality on an amiibo. To use the amiibo with another game that uses the read/write functionality, you will need to delete the game data from the amiibo.
However, even if you have game data stored, an amiibo can still be used in games that use the read functionality at any time.