Retailers recently started putting up Amiibos for preorder. Physical figurines which store data on your particular character.
As recently announced, the Amiibos will cost $13 each. The Wii U gamepad can read them and download their data into the game, but the Nintendo 3DS will require an extra peripheral in order to read Amiibos. The upcoming New 3DS does not require that peripheral to read Amiibos.